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Ndeye Fatou Diop
Ndeye Fatou Diop

Posted on • Edited on • Originally published at frontendjoy.com

101 React Tips & Tricks For Beginners To Experts ✨

#webdev #javascript #react #beginners

I have been working professionally with React for the past +5 years.

In this article, I share the 101 best tips & tricks I learned over the years.

Ready? Let's dive in 💪!

🎁 You can download an e-book version of this article for FREE here 👉 101 React Tips & Tricks

ℹ️ Notes:

  • This guide assumes a dsic familiarity with React and an understanding of the terms props, state, context, etc.
  • I tried to use Vanilla JS for most of the examples to keep things simple. If you're using TypeScript, you can easily adapt the code.
  • The code is not production-ready. Use at your own discretion.

Table of contents (Click to expand) ↕️

Category #1: Components organization 🧹

1. Use self-closing tags to keep your code compact 

// ❌ Bad: too verbose
<MyComponent></MyComponent>

// ✅ Good
<MyComponent/>
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2. Prefer fragments over DOM nodes (e.g., div, span, etc.) to group elements

In React, each component must return a single element. Instead of wrapping multiple elements in a <div> or <span>, use <Fragment> to keep your DOM neat and tidy.

❌ Bad: Using div clutters your DOM and may require more CSS code.

function Dashboard() {
  return (
    <div>
      <Header />
      <Main />
    </div>
  );
}
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✅ Good: <Fragment> wraps elements without affecting the DOM structure.

function Dashboard() {
  return (
    <Fragment>
      <Header />
      <Main />
    </Fragment>
  );
}
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3. Use React fragment shorthand <></> (except if you need to set a key)

❌ Bad: The code below is unnecessarily verbose.

<Fragment>
   <FirstChild />
   <SecondChild />
</Fragment>
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✅ Good: Unless, you need a key, <></> is more concise.

<>
   <FirstChild />
   <SecondChild />
</>

// Using a `Fragment` here is required because of the key.
function List({ users }) {
  return (
    <div>
      {users.map((user) => (
        <Fragment key={user.id}>
          <span>{user.name}</span>
          <span>{user.occupation}</span>
        </Fragment>
      ))}
    </div>
  );
}
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4. Prefer spreading props over accessing each one individually

❌ Bad: The code below is harder to read (especially at scale).

// We do `props…` all over the code.
function TodoList(props) {
  return (
    <div>
      {props.todos.map((todo) => (
        <div key={todo}>
          <button
            onClick={() => props.onSelectTodo(todo)}
            style={{
              backgroundColor: todo === props.selectedTodo ? "gold" : undefined,
            }}
          >
            <span>{todo}</span>
          </button>
        </div>
      ))}
    </div>
  );
}
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✅ Good: The code below is more concise.

function TodoList({ todos, selectedTodo, onSelectTodo }) {
  return (
    <div>
      {todos.map((todo) => (
        <div key={todo}>
          <button
            onClick={() => onSelectTodo(todo)}
            style={{
              backgroundColor: todo === selectedTodo ? "gold" : undefined,
            }}
          >
            <span>{todo}</span>
          </button>
        </div>
      ))}
    </div>
  );
}
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5. When setting default values for props, do it while destructuring them

❌ Bad: You may need to define the defaults in multiple places and introduce new variables.

function Button({ onClick, text, small, colorScheme }) {
  let scheme = colorScheme || "light";
  let isSmall = small || false;
  return (
    <button
      onClick={onClick}
      style={{
        color: scheme === "dark" ? "white" : "black",
        fontSize: isSmall ? "12px" : "16px",
      }}
    >
      {text ?? "Click here"}
    </button>
  );
}
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✅ Good: You can set all your defaults in one place at the top. This makes it easy for someone to locate them.

function Button({
  onClick,
  text = "Click here",
  small = false,
  colorScheme = "light",
}) {
  return (
    <button
      onClick={onClick}
      style={{
        color: colorScheme === "dark" ? "white" : "black",
        fontSize: small ? "12px" : "16px",
      }}
    >
      {text}
    </button>
  );
}
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6. Drop curly braces when passing string type props. 

// ❌ Bad: curly braces are not needed
<Button text={"Click me"} colorScheme={"dark"} />

// ✅ Good
<Button text="Click me" colorScheme="dark" />
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7. Ensure that value is a boolean before using value && <Component {...props}/> to prevent displaying unexpected values on the screen.

❌ Bad: When the list is empty, 0 will be printed on the screen.

export function ListWrapper({ items, selectedItem, setSelectedItem }) {
  return (
    <div className="list">
      {items.length && ( // `0` if the list is empty
        <List
          items={items}
          onSelectItem={setSelectedItem}
          selectedItem={selectedItem}
        />
      )}
    </div>
  );
}
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✅ Good: Nothing will be printed on the screen when there are no items.

export function ListWrapper({ items, selectedItem, setSelectedItem }) {
  return (
    <div className="list">
      {items.length > 0 && (
        <List
          items={items}
          onSelectItem={setSelectedItem}
          selectedItem={selectedItem}
        />
      )}
    </div>
  );
}
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8. Use functions (inline or not) to avoid polluting your scope with intermediate variables

❌ Bad: The variables gradeSum and gradeCount are cluttering the component's scope.

function Grade({ grades }) {
  if (grades.length === 0) {
    return <>No grades available.</>;
  }

  let gradeSum = 0;
  let gradeCount = 0;

  grades.forEach((grade) => {
    gradeCount++;
    gradeSum += grade;
  });

  const averageGrade = gradeSum / gradeCount;

  return <>Average Grade: {averageGrade}</>;
}
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✅ Good: The variables gradeSum and gradeCountare scoped within computeAverageGrade function.

function Grade({ grades }) {
  if (grades.length === 0) {
    return <>No grades available.</>;
  }

  const computeAverageGrade = () => {
    let gradeSum = 0;
    let gradeCount = 0;
    grades.forEach((grade) => {
      gradeCount++;
      gradeSum += grade;
    });
    return gradeSum / gradeCount;
  };

  return <>Average Grade: {computeAverageGrade()}</>;
}
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💡 Note: you can also define a function computeAverageGrade outside the component and call it inside it.

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9. Use curried functions to reuse logic (and properly memoize callback functions)

❌ Bad: The logic for updating a field is very repetitive.

function Form() {
  const [{ name, email }, setFormState] = useState({
    name: "",
    email: "",
  });

  return (
    <>
      <h1>Class Registration Form</h1>
      <form>
        <label>
          Name:{" "}
          <input
            type="text"
            value={name}
            onChange={(evt) =>
              setFormState((formState) => ({
                ...formState,
                name: evt.target.value,
              }))
            }
          />
        </label>
        <label>
          Email:{" "}
          <input
            type="email"
            value={email}
            onChange={(evt) =>
              setFormState((formState) => ({
                ...formState,
                email: evt.target.value,
              }))
            }
          />
        </label>
      </form>
    </>
  );
}
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✅ Good: Introduce createFormValueChangeHandler that returns the correct handler for each field.

Note: This trick is especially nice if you have the ESLint rule jsx-no-bind turned on. You can just wrap the curried function inside useCallback and "Voilà!".

function Form() {
  const [{ name, email }, setFormState] = useState({
    name: "",
    email: "",
  });

  const createFormValueChangeHandler = (field) => {
    return (event) => {
      setFormState((formState) => ({
        ...formState,
        [field]: event.target.value,
      }));
    };
  };

  return (
    <>
      <h1>Class Registration Form</h1>
      <form>
        <label>
          Name:{" "}
          <input
            type="text"
            value={name}
            onChange={createFormValueChangeHandler("name")}
          />
        </label>
        <label>
          Email:{" "}
          <input
            type="email"
            value={email}
            onChange={createFormValueChangeHandler("email")}
          />
        </label>
      </form>
    </>
  );
}
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10. Move data that doesn't rely on the component props/state outside of it for cleaner (and more efficient) code

❌ Bad: OPTIONS and renderOption don't need to be inside the component because they don't depend on any props or state.

Also, keeping them inside means we get new object references every time the component renders. If we were to pass renderOption to a child component wrapped in memo, it would break the memoization.

function CoursesSelector() {
  const OPTIONS = ["Maths", "Literature", "History"];
  const renderOption = (option: string) => {
    return <option>{option}</option>;
  };

  return (
    <select>
      {OPTIONS.map((opt) => (
        <Fragment key={opt}>{renderOption(opt)}</Fragment>
      ))}
    </select>
  );
}
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✅ Good: Move them out of the component to keep the component clean and references stable.

const OPTIONS = ["Maths", "Literature", "History"];
const renderOption = (option: string) => {
  return <option>{option}</option>;
};

function CoursesSelector() {
  return (
    <select>
      {OPTIONS.map((opt) => (
        <Fragment key={opt}>{renderOption(opt)}</Fragment>
      ))}
    </select>
  );
}
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💡 Note: In this example, you can simplify further by using the option element inline.

const OPTIONS = ["Maths", "Literature", "History"];

function CoursesSelector() {
  return (
    <select>
      {OPTIONS.map((opt) => (
        <option key={opt}>{opt}</option>
      ))}
    </select>
  );
}
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11. When storing the selected item from a list, store the item ID rather than the entire item

❌ Bad: If an item is selected but then it changes (i.e., we receive a completely new object reference for the same ID), or if the item is no longer present in the list, selectedItem will either retain an outdated value or become incorrect.

function ListWrapper({ items }) {
  // We are referencing the entire item
  const [selectedItem, setSelectedItem] = useState<Item | undefined>();

  return (
    <>
      {selectedItem != null && <div>{selectedItem.name}</div>}
      <List
        items={items}
        selectedItem={selectedItem}
        onSelectItem={setSelectedItem}
      />
    </>
  );
}
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✅ Good: We store the selected item by its ID (which should be stable). This ensures that even if the item is removed from the list or one of its properties changed, the UI should be correct.

function ListWrapper({ items }) {
  const [selectedItemId, setSelectedItemId] = useState<number | undefined>();
  // We derive the selected item from the list
  const selectedItem = items.find((item) => item.id === selectedItemId);

  return (
    <>
      {selectedItem != null && <div>{selectedItem.name}</div>}
      <List
        items={items}
        selectedItemId={selectedItemId}
        onSelectItem={setSelectedItemId}
      />
    </>
  );
}
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12. If you're frequently checking a prop's value before doing something, introduce a new component

❌ Bad: The code is cluttered because of all the user == null checks.

Here, we can't return early because of the rules of hooks.

function Posts({ user }) {
  // Due to the rules of hooks, `posts` and `handlePostSelect` must be declared before the `if` statement.
  const posts = useMemo(() => {
    if (user == null) {
      return [];
    }
    return getUserPosts(user.id);
  }, [user]);

  const handlePostSelect = useCallback(
    (postId) => {
      if (user == null) {
        return;
      }
      // TODO: Do something
    },
    [user]
  );

  if (user == null) {
    return null;
  }

  return (
    <div>
      {posts.map((post) => (
        <button key={post.id} onClick={() => handlePostSelect(post.id)}>
          {post.title}
        </button>
      ))}
    </div>
  );
}
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✅ Good: We introduce a new component, UserPosts, that takes a defined user and is much cleaner.

function Posts({ user }) {
  if (user == null) {
    return null;
  }

  return <UserPosts user={user} />;
}

function UserPosts({ user }) {
  const posts = useMemo(() => getUserPosts(user.id), [user.id]);

  const handlePostSelect = useCallback(
    (postId) => {
      // TODO: Do something
    },
    [user]
  );

  return (
    <div>
      {posts.map((post) => (
        <button key={post.id} onClick={() => handlePostSelect(post.id)}>
          {post.title}
        </button>
      ))}
    </div>
  );
}
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13. Use the CSS :empty pseudo-class to hide elements with no children

In the example below 👇, a wrapper takes children and adds a red border around them.

function PostWrapper({ children }) {
  return <div className="posts-wrapper">{children}</div>;
}
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.posts-wrapper {
  border: solid 1px red;
}
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❌ Problem: The border remains visible on the screen even if the children are empty (i.e., equal to null, undefined, etc.).

Red border

✅ Solution: Use the :empty CSS pseudo-class to ensure the wrapper is not displayed when it's empty.

.posts-wrapper:empty {
  display: none;
}
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14. Group all the state and context at the top of the component

When all the state and context are located at the top, it is easy to spot what can trigger a component re-render.

❌ Bad: State and context are scattered, making it hard to track.

function App() {
  const [email, setEmail] = useState("");
  const onEmailChange = (event) => {
    setEmail(event.target.value);
  };
  const [password, setPassword] = useState("");
  const onPasswordChange = (event) => {
    setPassword(event.target.value);
  };
  const theme = useContext(ThemeContext);

  return (
    <div className={`App ${theme}`}>
      <h1>Welcome</h1>
      <p>
        Email: <input type="email" value={email} onChange={onEmailChange} />
      </p>
      <p>
        Password:{" "}
        <input type="password" value={password} onChange={onPasswordChange} />
      </p>
    </div>
  );
}
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✅ Good: All state and context are grouped at the top, making it easy to spot.

function App() {
  const theme = useContext(ThemeContext);
  const [email, setEmail] = useState("");
  const [password, setPassword] = useState("");
  const onEmailChange = (event) => {
    setEmail(event.target.value);
  };
  const onPasswordChange = (event) => {
    setPassword(event.target.value);
  };

  return (
    <div className={`App ${theme}`}>
      <h1>Welcome</h1>
      <p>
        Email: <input type="email" value={email} onChange={onEmailChange} />
      </p>
      <p>
        Password:{" "}
        <input type="password" value={password} onChange={onPasswordChange} />
      </p>
    </div>
  );
}
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Category #2: Effective Design Patterns & Techniques 🛠 ️

15. Leverage the children props for cleaner code (and performance benefits)

Using the children props has several benefits:

  • Benefit #1: You can avoid prop drilling by passing props directly to children components instead of routing them through the parent.
  • Benefit #2: Your code is more extensible since you can easily modify children without changing the parent component.
  • Benefit #3: You can use this trick to avoid re-rendering "slow" components (see in the example below 👇).

❌ Bad: MyVerySlowComponent renders whenever Dashboard renders, which happens every time the current time updates. You can see it in the next image, where I use React Developer Tool's profiler.

function App() {
  // Some other logic…
  return (
    <Dashboard />
  );
}

function Dashboard() {
  const [currentTime, setCurrentTime] = useState(new Date());
  useEffect(() => {
    const intervalId = setInterval(() => {
      setCurrentTime(new Date());
    }, 1_000);
    return () => clearInterval(intervalId);
  }, []);

  return (
    <>
      <h1>{currentTime.toTimeString()}</h1>
      <MyVerySlowComponent />  {/* Renders whenever `Dashboard` renders */}
    </>
  );
}
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MyVerySlowComponent renders whenever Dashboard renders

✅ Good: MyVerySlowComponent doesn't render when Dashboard renders.

function App() {
  return (
    <Dashboard >
      <MyVerySlowComponent />
    </Dashboard>
  );
}

function Dashboard({ children }) {
  const [currentTime, setCurrentTime] = useState(new Date());
  useEffect(() => {
    const intervalId = setInterval(() => {
      setCurrentTime(new Date());
    }, 1_000);
    return () => clearInterval(intervalId);
  }, []);

  return (
    <>
      <h1>{currentTime.toTimeString()}</h1>
      {children}
    </>
  );
}
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MyVerySlowComponent doesn't render anymore

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16. Build composable code with compound components

Think of compound components as Lego blocks.

You piece them together to create a customized UI. These components work exceptionally well when creating libraries, resulting in both expressive and highly extendable code.

You can explore this pattern further here 👉 Compound Pattern

Example from reach.ui (Menu, MenuButton, MenuList, MenuLink are compound components)

<Menu>
  <MenuButton>
    Actions <span aria-hidden>▾</span>
  </MenuButton>
  <MenuList>
    <MenuItem onSelect={() => alert("Download")}>Download</MenuItem>
    <MenuItem onSelect={() => alert("Copy")}>Create a Copy</MenuItem>
    <MenuLink as="a" href="https://reacttraining.com/workshops/">
    Attend a Workshop
    </MenuLink>
  </MenuList>
</Menu>
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17. Make your code more extensible with render functions or component functions props

Let's say we want to display various lists, such as messages, profiles, or posts, and each one should be sortable.

To achieve this, we introduce a List component for reuse. There are two ways we can go around this:

❌ Bad: Option 1
List handles rendering each item and how they are sorted. This is problematic as it violates the Open Closed Principle. Whenever a new item type is added, this code will be modified.

✅ Good: Option 2
List takes render functions or component functions, invoking them only when needed.

You can find an example in this sandbox below 👇:

🏖 Sandbox

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18. When dealing with different cases, use value === case && <Component /> to avoid holding onto old state

❌ Problem: In the sandbox below, the counter doesn't reset when switching between Posts and Snippets. This happens because when rendering the same component, its state persists across type changes.

🏖 Sandbox

✅ Solution: Render a component based on the selectedType or use a key to force a reset when the type changes.

function App() {
  const [selectedType, setSelectedType] = useState<ResourceType>("posts");
  return (
    <>
      <Navbar selectedType={selectedType} onSelectType={setSelectedType} />
      {selectedType === "posts" && <Resource type="posts" />}
      {selectedType === "snippets" && <Resource type="snippets" />}
    </>
  );
}

// We use the `selectedType` as a key
function App() {
  const [selectedType, setSelectedType] = useState<ResourceType>("posts");
  return (
    <>
      <Navbar selectedType={selectedType} onSelectType={setSelectedType} />
      <Resource type={selectedType} key={selectedType} />
    </>
  );
}
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19. Always use error boundaries

By default, if your application encounters an error during rendering, the entire UI crashes 💥.

To prevent this, use error boundaries to:

  • Keep parts of your app functional even if an error occurs.
  • Display user-friendly error messages and optionally track errors.

💡 Tip: you can use the react-error-boundary library.

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Category #3: Keys & Refs 🗝️

20. Use crypto.randomUUID or Math.random to generate keys

JSX elements inside a map() call always need keys.

Suppose your elements don't already have keys. In that case, you can generate unique IDs using crypto.randomUUID, Math.random, or the uuid library.

Note: Beware that crypto.randomUUID is not defined in older browsers.

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21. Make sure your list items IDs are stable (i.e., they don't change between renders)

As much as possible, keys/IDs should be stable.

Otherwise, React may re-render some components uselessly, or selections will no longer be valid, like in the example below.

❌ Bad: selectedQuoteId changes whenever App renders, so there is never a valid selection.

function App() {
  const [quotes, setQuotes] = useState([]);
  const [selectedQuoteId, setSelectedQuoteId] = useState(undefined);

  // Fetch quotes
  useEffect(() => {
    const loadQuotes = () =>
      fetchQuotes().then((result) => {
        setQuotes(result);
      });
    loadQuotes();
  }, []);

  // Add ids: this is bad!!!
  const quotesWithIds = quotes.map((quote) => ({
    value: quote,
    id: crypto.randomUUID(),
  }));

  return (
    <List
      items={quotesWithIds}
      selectedItemId={selectedQuoteId}
      onSelectItem={setSelectedQuoteId}
    />
  );
}
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✅ Good: The IDs are added when we get the quotes.

function App() {
  const [quotes, setQuotes] = useState([]);
  const [selectedQuoteId, setSelectedQuoteId] = useState(undefined);

  // Fetch quotes and save with ID
  useEffect(() => {
    const loadQuotes = () =>
      fetchQuotes().then((result) => {
        // We add the `ids` as soon as we get the results
        setQuotes(
          result.map((quote) => ({
            value: quote,
            id: crypto.randomUUID(),
          }))
        );
      });
    loadQuotes();
  }, []);

  return (
    <List
      items={quotes}
      selectedItemId={selectedQuoteId}
      onSelectItem={setSelectedQuoteId}
    />
  );
}
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22. Strategically use the key attribute to trigger component re-renders

Want to force a component to re-render from scratch? Just change its key.

In the example below, we use this trick to reset the error boundary when switching to a new tab.

🏖 Sandbox

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23. Use a ref callback function for tasks such as monitoring size changes and managing multiple node elements.

Did you know you can pass a function to the ref attribute instead of a ref object?

Here's how it works:

  • When the DOM node is added to the screen, React calls the function with the DOM node as the argument.
  • When the DOM node is removed, React calls the function with null.

In the example below, we use this tip to skip the useEffect

❌ Before: Using useEffect to focus the input

function App() {
  const ref = useRef();

  useEffect(() => {
    ref.current?.focus();
  }, []);

  return <input ref={ref} type="text" />;
}
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✅ After: We focus on the input as soon as it is available.

function App() {
  const ref = useCallback((inputNode) => {
    inputNode?.focus();
  }, []);

  return <input ref={ref} type="text" />;
}
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Category #4: Organizing React code 🧩

24. Colocate React components with their assets (e.g., styles, images, etc.)

Always keep each React component with related assets, like styles and images.

  • This makes it easier to remove them when the component is no longer needed.
  • It also simplifies code navigation, as everything you need is in one place.

Components folder structure

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25. Limit your component file size

Big files with tons of components and exports can be confusing.

Plus, they tend to grow even bigger as more stuff gets added.

So, aim for a reasonable file size and split components into separate files when it makes sense.

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26. Limit the number of return statements in your functional component file

Multiple return statements in a functional component make it hard to see what the component is returning.

This was not a problem for class components where we could search for the render term.

A handy trick is to use arrow functions without braces when possible (VSCode has an action for this 😀).

❌ Bad: It is harder to spot the component return statement

function Dashboard({ posts, searchTerm, onPostSelect }) {
  const filteredPosts = posts.filter((post) => {
    return post.title.includes(searchTerm);
  });
  const createPostSelectHandler = (post) => {
    return () => {
      onPostSelect(post.id);
    };
  };
  return (
    <>
      <h1>Posts</h1>
      <ul>
        {filteredPosts.map((post) => {
          return (
            <li key={post.id} onClick={createPostSelectHandler(post)}>
              {post.title}
            </li>
          );
        })}
      </ul>
    </>
  );
}
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✅ Good: There is one return statement for the component

function Dashboard({ posts, searchTerm, onPostSelect, selectedPostId }) {
  const filteredPosts = posts.filter((post) => post.title.includes(searchTerm));
  const createPostSelectHandler = (post) => () => {
    onPostSelect(post.id);
  };
  return (
    <>
      <h1>Posts</h1>
      <ul>
        {filteredPosts.map((post) => (
          <li
            key={post.id}
            onClick={createPostSelectHandler(post)}
            style={{ color: post.id === selectedPostId ? "red" : "black" }}
          >
            {post.title}
          </li>
        ))}
      </ul>
    </>
  );
}
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27. Prefer named exports over default exports

I see default exports everywhere, and it makes me sad 🥲.

Let's compare the two approaches:

/// `Dashboard` is exported as the default component
export default function Dashboard(props) {
 /// TODO
}

/// `Dashboard` export is named
export function Dashboard(props) {
 /// TODO
}
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We now import the component like this:

/// Default export
import Dashboard from "/path/to/Dashboard"


/// Named export
import { Dashboard } from "/path/to/Dashboard"
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These are the problems with default exports:

  • If the component is renamed, the IDE won't automatically rename the export.

For example, if Dashboard is renamed into Console, we will have this:

/// In the default export case, the name is not changed
import Dashboard from "/path/to/Console"


/// In the named export case, the name is changed
import { Console } from "/path/to/Console"
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  • It's harder to see what is exported from a file with default exports.

For example, in the case of named imports, once I type import { } from "/path/to/file", I get autocompletion when I set my cursor inside the brackets.

  • Default exports are harder to re-export.

For example, if I wanted to re-export the Dashboard component from let's say an index file, I would have to do this:

export { default as Dashboard } from "/path/to/Dashboard"
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The solution is more straightforward with named exports.

export { Dashboard } from "/path/to/Dashboard"
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So, please default to named exports 🙏.

💡 Note: Even if you're using React lazy you can still use named exports. See an example here.

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Category #5: Efficient State Management 🚦

28. Never create a state for a value that can be derived from other state or props

More state = more trouble.

Every piece of state can trigger a re-render and make resetting the state a hassle.

So, if a value can be derived from state or props, skip adding a new state.

❌ Bad: filteredPosts doesn't need to be in the state.

function App({ posts }) {
  const [filters, setFilters] = useState();
  const [filteredPosts, setFilteredPosts] = useState([]);

  useEffect(
    () => {
      setFilteredPosts(filterPosts(posts, filters));
    },
    [posts, filters]
  );

  return (
    <Dashboard>
      <Filters filters={filters} onFiltersChange={setFilters} />
      {filteredPosts.length > 0 && <Posts posts={filteredPosts} />}
    </Dashboard>
  );
}
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✅ Good: filteredPosts is derived from posts and filters.

function App({ posts }) {
  const [filters, setFilters] = useState({});
  const filteredPosts = filterPosts(posts, filters)

  return (
    <Dashboard>
      <Filters filters={filters} onFiltersChange={setFilters} />
      {filteredPosts.length > 0 && <Posts posts={filteredPosts} />}
    </Dashboard>
  );
}
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29. Keep the state at the lowest level necessary to minimize re-renders

Whenever the state changes inside a component, React re-renders the component and all its children (there is an exception with children wrapped in memo).

This happens even if those children don't use the changed state. To minimize re-renders, move the state down the component tree as far as possible.

❌ Bad: When sortOrder changes, both LeftSidebar and RightSidebar re-render.

function App() {
  const [sortOrder, setSortOrder] = useState("popular");
  return (
    <div className="App">
      <LeftSidebar />
      <Main sortOrder={sortOrder} setSortOrder={setSortOrder} />
      <RightSidebar />
    </div>
  );
}

function Main({ sortOrder, setSortOrder }) {
  return (
    <div>
      <Button
        onClick={() => setSortOrder("popular")}
        active={sortOrder === "popular"}
      >
        Popular
      </Button>
      <Button
        onClick={() => setSortOrder("latest")}
        active={sortOrder === "latest"}
      >
        Latest
      </Button>
    </div>
  );
}
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✅ Good: sortOrder change will only affect Main.

function App() {
  return (
    <div className="App">
      <LeftSidebar />
      <Main />
      <RightSidebar />
    </div>
  );
}

function Main() {
  const [sortOrder, setSortOrder] = useState("popular");
  return (
    <div>
      <Button
        onClick={() => setSortOrder("popular")}
        active={sortOrder === "popular"}
      >
        Popular
      </Button>
      <Button
        onClick={() => setSortOrder("latest")}
        active={sortOrder === "latest"}
      >
        Latest
      </Button>
    </div>
  );
}
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30. Clarify the distinction between the initial state and the current state

❌ Bad: It's unclear that sortOrder is just the initial value, which may lead to confusion or errors in state management.

function Main({ sortOrder }) {
  const [internalSortOrder, setInternalSortOrder] = useState(sortOrder);
  return (
    <div>
      <Button
        onClick={() => setInternalSortOrder("popular")}
        active={internalSortOrder === "popular"}
      >
        Popular
      </Button>
      <Button
        onClick={() => setInternalSortOrder("latest")}
        active={internalSortOrder === "latest"}
      >
        Latest
      </Button>
    </div>
  );
}
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✅ Good: Naming is clear about what is the initial state and what is current.

function Main({ initialSortOrder }) {
  const [sortOrder, setSortOrder] = useState(initialSortOrder);
  return (
    <div>
      <Button
        onClick={() => setSortOrder("popular")}
        active={sortOrder === "popular"}
      >
        Popular
      </Button>
      <Button
        onClick={() => setSortOrder("latest")}
        active={sortOrder === "latest"}
      >
        Latest
      </Button>
    </div>
  );
}
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31. Update state based on the previous state, especially when memoizing with useCallback

React allows you to pass an updater function to the set function from useState.

This updater function uses the current state to calculate the next state.

I use this behavior whenever I need to update the state based on the previous state, especially inside functions wrapped with useCallback. In fact, this approach prevents the need to have the state as one of the hook dependencies.

❌ Bad: handleAddTodo and handleRemoveTodo change whenever todos changes.

function App() {
  const [todos, setToDos] = useState([]);
  const handleAddTodo = useCallback(
    (todo) => {
      setToDos([...todos, todo]);
    },
    [todos]
  );

  const handleRemoveTodo = useCallback(
    (id) => {
      setToDos(todos.filter((todo) => todo.id !== id));
    },
    [todos]
  );

  return (
    <div className="App">
      <TodoInput onAddTodo={handleAddTodo} />
      <TodoList todos={todos} onRemoveTodo={handleRemoveTodo} />
    </div>
  );
}
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✅ Good: handleAddTodo and handleRemoveTodo remain the same even when todos changes.

function App() {
  const [todos, setToDos] = useState([]);
  const handleAddTodo = useCallback((todo) => {
    setToDos((prevTodos) => [...prevTodos, todo]);
  }, []);

  const handleRemoveTodo = useCallback((id) => {
    setToDos((prevTodos) => prevTodos.filter((todo) => todo.id !== id));
  }, []);

  return (
    <div className="App">
      <TodoInput onAddTodo={handleAddTodo} />
      <TodoList todos={todos} onRemoveTodo={handleRemoveTodo} />
    </div>
  );
}
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32. Use functions in useState for lazy initialization and performance gains, as they are invoked only once.

Using a function in useState ensures the initial state is computed only once.

This can improve performance, especially when the initial state is derived from an "expensive" operation like reading from local storage.

❌ Bad: We read the theme from local storage every time the component renders

const THEME_LOCAL_STORAGE_KEY = "101-react-tips-theme";

function PageWrapper({ children }) {
  const [theme, setTheme] = useState(
    localStorage.getItem(THEME_LOCAL_STORAGE_KEY) || "dark"
  );

  const handleThemeChange = (theme) => {
    setTheme(theme);
    localStorage.setItem(THEME_LOCAL_STORAGE_KEY, theme);
  };

  return (
    <div
      className="page-wrapper"
      style={{ background: theme === "dark" ? "black" : "white" }}
    >
      <div className="header">
        <button onClick={() => handleThemeChange("dark")}>Dark</button>
        <button onClick={() => handleThemeChange("light")}>Light</button>
      </div>
      <div>{children}</div>
    </div>
  );
}
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✅ Good: We only read from the local storage when the component mounts.

function PageWrapper({ children }) {
  const [theme, setTheme] = useState(
    () => localStorage.getItem(THEME_LOCAL_STORAGE_KEY) || "dark"
  );

  const handleThemeChange = (theme) => {
    setTheme(theme);
    localStorage.setItem(THEME_LOCAL_STORAGE_KEY, theme);
  };

  return (
    <div
      className="page-wrapper"
      style={{ background: theme === "dark" ? "black" : "white" }}
    >
      <div className="header">
        <button onClick={() => handleThemeChange("dark")}>Dark</button>
        <button onClick={() => handleThemeChange("light")}>Light</button>
      </div>
      <div>{children}</div>
    </div>
  );
}
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33. Use react context for broadly needed, static state to prevent prop drilling

I will use React context whenever I have some data that:

  • Is needed in multiple places (e.g., theme, current user, etc.)
  • Is mostly static or read-only (i.e., the user can't/doesn't change the data often)

This approach helps avoid prop drilling (i.e., passing down data or state through multiple layers of the component hierarchy).

See an example in the sandbox below 👇.

🏖 Sandbox

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34. React Context: Split your context into parts that change frequently and those that change infrequently to enhance app performance

One challenge with React context is that all components consuming the context re-render whenever the context data changes, even if they don't use the part of the context that changed 🤦‍♀️.

A solution? Use separate contexts.

In the example below, we've created two contexts: one for actions (which are constant) and another for state (which can change).

🏖 Sandbox

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35. React Context: Introduce a Provider component when the value computation is not straightforward

❌ Bad: There is too much logic inside App to manage the theme.

const THEME_LOCAL_STORAGE_KEY = "101-react-tips-theme";
const DEFAULT_THEME = "light";

const ThemeContext = createContext({
  theme: DEFAULT_THEME,
  setTheme: () => null,
})

function App() {
  const [theme, setTheme] = useState(
    () => localStorage.getItem(THEME_LOCAL_STORAGE_KEY) || DEFAULT_THEME
  );
  useEffect(() => {
    if(theme !== "system") {
      updateRootElementTheme(theme)
      return;
    }

    // We need to get the class to apply based on the system theme
    const systemTheme = window.matchMedia("(prefers-color-scheme: dark)")
        .matches
        ? "dark"
        : "light"

    updateRootElementTheme(systemTheme)

    // Then watch for changes in the system theme and update the root element accordingly
    const darkThemeMq = window.matchMedia("(prefers-color-scheme: dark)");
    const listener = (event) => {
      updateRootElementTheme(event.matches ? "dark" : "light")
    };
    darkThemeMq.addEventListener("change", listener);
    return () => darkThemeMq.removeEventListener("change", listener);
  }, [theme]);

  const themeContextValue = {
    theme,
    setTheme: (theme) => {
      localStorage.setItem(THEME_LOCAL_STORAGE_KEY, theme);
      setTheme(theme);
    }
  }

  const [selectedPostId, setSelectedPostId] = useState(undefined);
  const onPostSelect = (postId) => {
    // TODO: some logging
    setSelectedPostId(postId);
  };

  const posts = useSWR("/api/posts", fetcher);

  return (
    <div className="App">
      <ThemeContext.Provider value={themeContextValue}>
        <Dashboard
          posts={posts}
          onPostSelect={onPostSelect}
          selectedPostId={selectedPostId}
        />
      </ThemeContext.Provider>
    </div>
  );
}
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✅ Good: The theme logic is encapsulated in ThemeProvider

function App() {
  const [selectedPostId, setSelectedPostId] = useState(undefined);
  const onPostSelect = (postId) => {
    // TODO: some logging
    setSelectedPostId(postId);
  };

  const posts = useSWR("/api/posts", fetcher);

  return (
    <div className="App">
      <ThemeProvider>
        <Dashboard
          posts={posts}
          onPostSelect={onPostSelect}
          selectedPostId={selectedPostId}
        />
      </ThemeProvider>
    </div>
  );
}


function ThemeProvider({ children }) {
  const [theme, setTheme] = useState(
    () => localStorage.getItem(THEME_LOCAL_STORAGE_KEY) || DEFAULT_THEME
  );
  useEffect(() => {
    if (theme !== "system") {
      updateRootElementTheme(theme);
      return;
    }

    // We need to get the class to apply based on the system theme
    const systemTheme = window.matchMedia("(prefers-color-scheme: dark)")
      .matches
      ? "dark"
      : "light";

    updateRootElementTheme(systemTheme);

    // Then watch for changes in the system theme and update the root element accordingly
    const darkThemeMq = window.matchMedia("(prefers-color-scheme: dark)");
    const listener = (event) => {
      updateRootElementTheme(event.matches ? "dark" : "light");
    };
    darkThemeMq.addEventListener("change", listener);
    return () => darkThemeMq.removeEventListener("change", listener);
  }, [theme]);

  const themeContextValue = {
    theme,
    setTheme: (theme) => {
      localStorage.setItem(THEME_LOCAL_STORAGE_KEY, theme);
      setTheme(theme);
    },
  };

  return (
    <div className="App">
      <ThemeContext.Provider value={themeContextValue}>
        {children}
      </ThemeContext.Provider>
    </div>
  );
}
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36. Consider using the useReducer hook as a lightweight state management solution

Whenever I have too many values in my state or a complex state and don't want to rely on external libraries, I will reach for useReducer.

It's especially effective when combined with context for broader state management needs.

Example: See #Tip 34.

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37. Simplify state updates with useImmer or useImmerReducer

With hooks like useState and useReducer, the state must be immutable (i.e., all changes need to create a new state vs. modifying the current one).

This is often cumbersome to achieve.

This is where useImmer and useImmerReducer offer a simpler alternative. They allow you to write "mutable" code automatically converted to immutable updates.

❌ Tedious: We must carefully ensure we're creating a new state object.

export function App() {
  const [{ email, password }, setState] = useState({
    email: "",
    password: "",
  });
  const onEmailChange = (event) => {
    setState((prevState) => ({ ...prevState, email: event.target.value }));
  };
  const onPasswordChange = (event) => {
    setState((prevState) => ({ ...prevState, password: event.target.value }));
  };

  return (
    <div className="App">
      <h1>Welcome</h1>
      <p>
        Email: <input type="email" value={email} onChange={onEmailChange} />
      </p>
      <p>
        Password:{" "}
        <input type="password" value={password} onChange={onPasswordChange} />
      </p>
    </div>
  );
}
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✅ More straightforward: We can directly modify draftState.

import { useImmer } from "use-immer";

export function App() {
  const [{ email, password }, setState] = useImmer({
    email: "",
    password: "",
  });
  const onEmailChange = (event) => {
    setState((draftState) => {
      draftState.email = event.target.value;
    });
  };
  const onPasswordChange = (event) => {
    setState((draftState) => {
      draftState.password = event.target.value;
    });
  };

  /// Rest of logic
}
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38. Use Redux (or another state management solution) for complex client-side state accessed across multiple components

I turn to Redux whenever:

  • I have a complex FE app with a lot of shared client-side state (for example, dashboard apps)
  • I want the user to be able to go back in time and revert changes
  • I don't want my components to re-render unnecessarily like they can with React context
  • I have too many contexts that start getting out of control

For a streamlined experience, I recommend using redux-tooltkit.

💡 Note: You can also consider other alternatives to Redux, such as Zustand or Recoil.

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39. Redux: Use Redux DevTools to debug your state

The Redux DevTools browser extension is an useful tool for debugging your Redux projects.

It allows you to visualize your state and actions in real-time, maintain state persistence across refreshes, and much more.

To understand its use, watch this great YouTube video.

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Category #6: React Code Optimization 🚀

40. Prevent unnecessary re-renders with memo

When dealing with components that are costly to render and their parent components frequently update, wrapping them in memo can be a game changer.

memo ensures that a component only re-renders when its props have changed, not simply because its parent re-rendered.

In the example below, I get some data from the server through useGetDashboardData. If the posts didn't change, wrapping ExpensiveList in memo will prevent it from re-rendering when other parts of the data update.

export function App() {
  const { profileInfo, posts } = useGetDashboardData();
  return (
    <div className="App">
      <h1>Dashboard</h1>
      <Profile data={profileInfo} />
      <ExpensiveList posts={posts} />
    </div>
  );
}

const ExpensiveList = memo(
  ({ posts }) => {
    /// Rest of implementation
  }
);
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💡: This tip may be irrelevant once React compiler gets stable 😅.

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41. Specify an equality function with memo to instruct React on how to compare the props.

By default, memouses Object.is to compare each prop with its previous value.

However, specifying a custom equality function can be more efficient than default comparisons or re-rendering for more complex or specific scenarios.

Example 👇

const ExpensiveList = memo(
  ({ posts }) => {
    return <div>{JSON.stringify(posts)}</div>;
  },
  (prevProps, nextProps) => {
    // Only re-render if the last post or the list size changes
    const prevLastPost = prevProps.posts[prevProps.posts.length - 1];
    const nextLastPost = nextProps.posts[nextProps.posts.length - 1];
    return (
      prevLastPost.id === nextLastPost.id &&
      prevProps.posts.length === nextProps.posts.length
    );
  }
)
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42. Prefer named functions over arrow functions when declaring a memoized component

When defining memoized components, using named functions instead of arrow functions can improve clarity in React DevTools.

Arrow functions often result in generic names like _c2, making debugging and profiling more difficult.

❌ Bad: Using arrow functions for memoized components results in less informative names in React DevTools.

const ExpensiveList = memo(
  ({ posts }) => {
    /// Rest of implementation
  }
);
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ExpensiveList name is not visible

✅ Good: The component's name will be visible in DevTools.

const ExpensiveList = memo(
  function ExpensiveListFn({ posts }) {
    /// Rest of implementation
  }
);
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You can see ExpensiveListFn in DevTools

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43. Cache expensive computations or preserve references with useMemo

I will generally useMemo:

  • When I have expensive computations that should not be repeated on each render.
  • If the computed value is a non-primitive value that is used as a dependency in hooks like useEffect.
  • The computed non-primitive value will be passed as a prop to a component wrapped in memo; otherwise, this will break the memoization since React uses Object.is to detect whether props changed.

❌ Bad: The memo for ExpensiveList does not prevent re-renders because styles are recreated on every render.

export function App() {
  const { profileInfo, posts, baseStyles } = useGetDashboardData();
  // We get a new `styles` object on every render
  const styles = { ...baseStyles, padding: "10px" };
  return (
    <div className="App">
      <h1>Dashboard</h1>
      <Profile data={profileInfo} />
      <ExpensiveList posts={posts} styles={styles} />
    </div>
  );
}

const ExpensiveList = memo(
  function ExpensiveListFn({ posts, styles }) {
    /// Rest of implementation
  }
);
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✅ Good: The use of useMemo ensures styles only changes when baseStyles changes, allowing memo to effectively prevent unnecessary re-renders.

export function App() {
  const { profileInfo, posts, baseStyles } = useGetDashboardData();
  // We get a new `styles` object only if `baseStyles` changes
  const styles = useMemo(
    () => ({ ...baseStyles, padding: "10px" }),
    [baseStyles]
  );
  return (
    <div className="App">
      <h1>Dashboard</h1>
      <Profile data={profileInfo} />
      <ExpensiveList posts={posts} styles={styles} />
    </div>
  );
}
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44. Use useCallback to memoize functions

useCallback is similar to useMemo but is designed explicitly for memoizing functions.

❌ Bad: Whenever the theme changes, handleThemeChange will be called twice, and we will push logs to the server twice.

function useTheme() {
  const [theme, setTheme] = useState("light");

  // `handleThemeChange` changes on every render
  // As a result, the effect will be triggered after each render
  const handleThemeChange = (newTheme) => {
    pushLog(["Theme changed"], {
      context: {
        theme: newTheme,
      },
    });
    setTheme(newTheme);
  };

  useEffect(() => {
    const dqMediaQuery = window.matchMedia("(prefers-color-scheme: dark)");
    handleThemeChange(dqMediaQuery.matches ? "dark" : "light");
    const listener = (event) => {
      handleThemeChange(event.matches ? "dark" : "light");
    };
    dqMediaQuery.addEventListener("change", listener);
    return () => {
      dqMediaQuery.removeEventListener("change", listener);
    };
  }, [handleThemeChange]);

  return theme;
}
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✅ Good: Wrapping handleThemeChange in useCallback ensures that it is recreated only when necessary, reducing unnecessary executions.

const handleThemeChange = useCallback((newTheme) => {
    pushLog(["Theme changed"], {
      context: {
        theme: newTheme,
      },
    });
    setTheme(newTheme);
  }, []);
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45. Memoize callbacks or values returned from utility hooks to avoid performance issues

When you create a custom hook to share with others, memoizing the returned values and functions is crucial.

This practice makes your hook more efficient and prevents unnecessary performance issues for anyone using it.

❌ Bad: loadData is not memoized and creates performance issues.

function useLoadData(fetchData) {
  const [result, setResult] = useState({
    type: "notStarted",
  });

  async function loadData() {
    setResult({ type: "loading" });
    try {
      const data = await fetchData();
      setResult({ type: "loaded", data });
    } catch (err) {
      setResult({ type: "error", error: err });
    }
  }

  return { result, loadData };
}
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✅ Good: We memoize everything so there are no unexpected performance issues.

function useLoadData(fetchData) {
  const [result, setResult] = useState({
    type: "notStarted",
  });

  // Wrap in `useRef` and use the `ref` value so the function never changes
  const fetchDataRef = useRef(fetchData);
  useEffect(() => {
    fetchDataRef.current = fetchData;
  }, [fetchData]);

  // Wrap in `useCallback` and use the `ref` value so the function never changes
  const loadData = useCallback(async () => {
    setResult({ type: "loading" });
    try {
      const data = await fetchDataRef.current();
      setResult({ type: "loaded", data });
    } catch (err) {
      setResult({ type: "error", error: err });
    }
  }, []);

  return useMemo(() => ({ result, loadData }), [result, loadData])
}
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46. Leverage lazy loading and Suspense to make your apps load faster

When you're building your app, consider using lazy loading and Suspense for code that is:

  • Expensive to load.
  • Only relevant to some users (like premium features).
  • Not immediately necessary for the initial user interaction.

In the sandbox below 👇, the Slider assets (JS + CSS) only load after you click on a card.

🏖 Sandbox


Slider assets only load when needed

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47. Throttle your network to simulate a slow network

Did you know you can simulate slow internet connections directly in Chrome?

This is especially useful when:

  • Customers report slow loading times that you can't replicate on your faster network.
  • You're implementing lazy loading and want to observe how files load under slower conditions to ensure appropriate loading states.


Throttling network requests to observe lazy loading

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48. Use react-window or react-virtuoso to efficiently render lists

Never render a long list of items all at once—such as chat messages, logs, or infinite lists.

Doing so can cause the browser to freeze.

Instead, virtualize the list. This means rendering only the subset of items likely to be visible to the user.

Libraries like react-window, react-virtuoso or @tanstack/react-virtual are designed for this purpose.

❌ Bad: NonVirtualList renders all 50,000 log lines simultaneously, even if they aren't visible.

function NonVirtualList({ items }) {
  return (
    <div style={{ height: "100%" }}>
      {items.map((log, index) => (
        <div
          key={log.id}
          style={{
            padding: "5px",
            borderBottom:
              index === items.length - 1 ? "none" : "1px solid #ccc",
          }}
        >
          <LogLine log={log} index={index} />
        </div>
      ))}
    </div>
  );
}
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✅ Good: VirtualList renders only the items likely to be visible.

function VirtualList({ items }) {
  return (
    <Virtuoso
      style={{ height: "100%" }}
      data={items}
      itemContent={(index, log) => (
        <div
          key={log.id}
          style={{
            padding: "5px",
            borderBottom:
              index === items.length - 1 ? "none" : "1px solid #ccc",
          }}
        >
          <LogLine log={log} index={index} />
        </div>
      )}
    />
  );
}
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You can switch between the two options in the sandbox below and notice how bad the app performs when NonVirtualList is used 👇.

🏖 Sandbox

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Category #7: Debugging React code 🐞

49. Use StrictMode to catch bugs in your components before deploying them to production

Using StrictMode is a proactive way to detect potential issues in your application during development.

It helps identify problems such as:

  • Incomplete cleanup in effects, like forgetting to release resources.
  • Impurities in React components, ensuring they return consistent JSX given the same inputs (props, state, and context).

The example below shows a bug because clearInterval is never called. StrictMode helps catch this by running the effect twice, which creates two intervals.

🏖 Sandbox

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50. Install the React Developer Tools browser extension to view/edit your components and detect performance issues

React Developer Tools is a must extension (Chrome, Firefox).

This extension lets you:

  • Visualize and delve into the details of your React components, examining everything from props to state.
  • Directly modify a component's state or props to see how changes affect behavior and rendering.
  • Profile your application to identify when and why components are re-rendering, helping you spot performance issues.
  • Etc.

💡 Learn how to use it in this great guide.

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51. React DevTools Components: Highlight components that render to identify potential issues

I will use this trick whenever I suspect that my app has performance issues. You can highlight the components that render to detect potential problems (e.g., too many renders).

The gif below shows that the FollowersListFn component re-renders whenever the time changes, which is wrong.


Highlight updates when components render.

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52. Leverage useDebugValue in your custom hooks for better visibility in React DevTools

useDebugValue can be a handy tool for adding descriptive labels to your custom hooks in React DevTools.

This makes it easier to monitor their states directly from the DevTools interface.

For instance, consider this custom hook I use to fetch and display the current time, updated every second:

function useCurrentTime(){
  const [time, setTime] = useState(new Date());

  useEffect(() => {
    const intervalId = setInterval(() => {
      setTime(new Date());
    }, 1_000);
    return () => clearInterval(intervalId);
  }, [setTime]);

  return time;
}
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❌ Bad: Without useDebugValue, the actual time value isn't immediately visible; you'd need to expand the CurrentTime hook:


Current time not quickly visible on the devtools

✅ Good: With useDebugValue, the current time is readily visible:

useDebugValue(time)
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Current time quickly visible on the devtools

Note: Use useDebugValue judiciously. It's best reserved for complex hooks in shared libraries where understanding the internal state is crucial.

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53. Use the why-did-you-render library to track component rendering and identify potential performance bottlenecks

Sometimes, a component re-renders, and it's not immediately clear why 🤦‍♀️.

While React DevTools is helpful, in large apps, it might only provide vague explanations like "hook #1 rendered," which can be useless.


App rendering because of hook 1 change

In such cases, you can turn to the why-did-you-render library. It offers more detailed insights into why components re-render, helping to pinpoint performance issues more effectively.

I made an example in the sandbox below 👇. Thanks to this library, we can find the issue with the FollowersList component.

🏖 Sandbox


why-did-you-render console logs

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54. Hide logs during the second render in Strict Mode

StrictMode helps catch bugs early in your application's development.

However, since it causes components to render twice, this can result in duplicated logs, which might clutter your console.

You can hide logs during the second render in Strict Mode to address this.

Check out how to do it in the gif below 👇:

Hide logs during the second render in Strict Mode

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Category #8: Testing React code 🧪

55. Use React Testing Library to test your React components effectively

Want to test your React apps?

Make sure to use @testing-library/react.

You can find a minimal example here.

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56. React Testing Library: Use testing playground to effortlessly create queries

Struggling to decide which queries to use in your tests?

Consider using testing playground to quickly generate them from your component's HTML.

Here are two ways to leverage it:

Option #1: Use screen.logTestingPlaygroundURL() in your test. This function generates a URL that opens the Testing Playground tool with the HTML of your component already loaded.

Using screen.logTestingPlaygroundURL

Option #2: Install Testing Playground Chrome extension. This extension allows you to hover over elements in your app directly in the browser to find the best queries for testing them.

Using testing playground extension

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57. Conduct end-to-end tests with Cypress or Playwright

Need to conduct end-to-end tests?

Make sure to check out Cypress or Playwright.

Note: Playwright's support for components is experimental at the time of writing.

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58. Use MSW to mock network requests in your tests

Sometimes, your tests need to make network requests.

Rather than implementing your own mocks (or, God forbid, making actual network requests 😅), consider using MSW (Mock Service Worker) to handle your API responses.

MSW allows you to intercept and manipulate network interactions directly in your tests, providing a robust and straightforward solution for simulating server responses without affecting live servers.

This approach helps maintain a controlled and predictable testing environment, enhancing the reliability of your tests.

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Category #9: React hooks 🎣

59. Make sure you perform any required cleanup in your useEffect hooks

Always return a cleanup function in your useEffect hooks if you're setting up anything that needs to be cleaned up later.

This could be anything from ending a chat session to closing a database connection.

Neglecting this step can lead to poor resource usage and potential memory leaks.

❌ Bad: This example sets an interval. But we never clear it, which means it keeps running even after the component is unmounted.

function Timer() {
  const [time, setTime] = useState(new Date());
  useEffect(() => {
    setInterval(() => {
      setTime(new Date());
    }, 1_000);
  }, []);

  return <>Current time {time.toLocaleTimeString()}</>;
}
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✅ Good: The interval is properly cleared when the component unmounts.

function Timer() {
  const [time, setTime] = useState(new Date());
  useEffect(() => {
    const intervalId = setInterval(() => {
      setTime(new Date());
    }, 1_000);
    // We clear the interval
    return () => clearInterval(intervalId);
  }, []);

  return <>Current time {time.toLocaleTimeString()}</>;
}
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60. Use refs for accessing DOM elements

You should never manipulate the DOM directly with React.

Methods like document.getElementById and document.getElementsByClassName are forbidden since React should access/manipulate the DOM.

So, what should you do when you need access to DOM elements?

You can use the useRef hook, like in the example below, where we need access to the canvas element.

🏖 Sandbox

Note: We could have added an ID to the canvas and used document.getElementById, but this is not recommended.

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61. Use refs to preserve values across re-renders

If you have mutable values in your React component that aren't stored in the state, you'll notice that changes to these values don't persist through re-renders.

This happens unless you save them globally.

You might consider putting these values in the state. However, if they are irrelevant to the rendering, doing so can cause unnecessary re-renders, which wastes performance.

This is where useRef also shines.

In the example below, I want to stop the timer when the user clicks on some button. For that, I need to store the intervalId somewhere.

❌ Bad: The example below won't work as intended because intervalId gets reset with every component re-render.

function Timer() {
  const [time, setTime] = useState(new Date());
  let intervalId;

  useEffect(() => {
    intervalId = setInterval(() => {
      setTime(new Date());
    }, 1_000);
    return () => clearInterval(intervalId);
  }, []);

  const stopTimer = () => {
    intervalId && clearInterval(intervalId);
  };

  return (
    <>
      <>Current time: {time.toLocaleTimeString()} </>
      <button onClick={stopTimer}>Stop timer</button>
    </>
  );
}
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✅ Good: By using useRef, we ensure that the interval ID is preserved between renders.

function Timer() {
  const [time, setTime] = useState(new Date());
  const intervalIdRef = useRef();
  const intervalId = intervalIdRef.current;

  useEffect(() => {
    const interval = setInterval(() => {
      setTime(new Date());
    }, 1_000);
    intervalIdRef.current = interval;
    return () => clearInterval(interval);
  }, []);

  const stopTimer = () => {
    intervalId && clearInterval(intervalId);
  };

  return (
    <>
      <>Current time: {time.toLocaleTimeString()} </>
      <button onClick={stopTimer}>Stop timer</button>
    </>
  );
}
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62. Prefer named functions over arrow functions within hooks such as useEffect to easily find them in React Dev Tools

If you have many hooks, finding them in React DevTools can be challenging.

One trick is to use named functions so you can quickly spot them.

❌ Bad: It's hard to find the specific effect among many hooks.

function HelloWorld() {
  useEffect(() => {
    console.log("🚀 ~ Hello, I just got mounted")
  }, []);

  return <>Hello World</>;
}
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Effect has no associated name

✅ Good: You can quickly spot the effect.

function HelloWorld() {
  useEffect(function logOnMount() {
    console.log("🚀 ~ Hello, I just got mounted");
  }, []);

  return <>Hello World</>;
}
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Effect with associated name

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63. Encapsulate logic with custom hooks

Let's say I have a component that gets the theme from the user's dark mode preferences and uses it inside the app.

It's better to extract the logic that returns the theme into a custom hook (to reuse it and keep the component clean).

❌ Bad: App is overcrowded

function App() {
  const [theme, setTheme] = useState("light");

  useEffect(() => {
    const dqMediaQuery = window.matchMedia("(prefers-color-scheme: dark)");
    setTheme(dqMediaQuery.matches ? "dark" : "light");
    const listener = (event) => {
      setTheme(event.matches ? "dark" : "light");
    };
    dqMediaQuery.addEventListener("change", listener);
    return () => {
      dqMediaQuery.removeEventListener("change", listener);
    };
  }, []);

  return (
    <div className={`App ${theme === "dark" ? "dark" : ""}`}>Hello Word</div>
  );
}
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✅ Good: App is much simpler, and we can reuse the logic

function App() {
  const theme = useTheme();

  return (
    <div className={`App ${theme === "dark" ? "dark" : ""}`}>Hello Word</div>
  );
}

// Custom hook that can be reused
function useTheme() {
  const [theme, setTheme] = useState("light");

  useEffect(() => {
    const dqMediaQuery = window.matchMedia("(prefers-color-scheme: dark)");
    setTheme(dqMediaQuery.matches ? "dark" : "light");
    const listener = (event) => {
      setTheme(event.matches ? "dark" : "light");
    };
    dqMediaQuery.addEventListener("change", listener);
    return () => {
      dqMediaQuery.removeEventListener("change", listener);
    };
  }, []);

  return theme;
}
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64. Prefer functions over custom hooks

Never put logic inside a hook when a function can be used 🛑.

In effect:

  • Hooks can only be used inside other hooks or components, whereas functions can be used everywhere.
  • Functions are simpler than hooks.
  • Functions are easier to test.
  • Etc.

❌ Bad: The useLocale hook is unnecessary since it doesn't need to be a hook. It doesn't use other hooks like useEffect, useState, etc.

function App() {
  const locale = useLocale();
  return (
    <div className="App">
      <IntlProvider locale={locale}>
        <BlogPost post={EXAMPLE_POST} />
      </IntlProvider>
    </div>
  );
}

function useLocale() {
  return window.navigator.languages?.[0] ?? window.navigator.language;
}
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✅ Good: Create a function getLocale instead

function App() {
  const locale = getLocale();
  return (
    <div className="App">
      <IntlProvider locale={locale}>
        <BlogPost post={EXAMPLE_POST} />
      </IntlProvider>
    </div>
  );
}

function getLocale() {
  return window.navigator.languages?.[0] ?? window.navigator.language;
}
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65. Prevent visual UI glitches by using the useLayoutEffect hook

When an effect isn't caused by a user interaction, the user will see the UI before the effect runs (often briefly).

As a result, if the effect modifies the UI, the user will see the initial UI version very quickly before seeing the updated one, creating a visual glitch.

Using useLayoutEffect ensures the effect runs synchronously after all DOM mutations, preventing the initial render glitch.

In the sandbox below, we want the width to be equally distributed between the columns (I know this can be done in CSS, but I need an example 😅).

With useEffect, you can see briefly at the beginning that the table is changing. The columns are rendered with their default size before being adjusted to their correct size.

🏖 Sandbox

If you're looking for another great usage, check out this post.

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66. Generate unique IDs for accessibility attributes with the useId hook

Tired of coming up with IDs or having them clash?

You can use the useId hook to generate a unique ID inside your React component and ensure your app is accessible.

Example

function Form() {
  const id = useId();
  return (
    <div className="App">
      <div>
        <label>
          Name{" "}
          <input type="text" aria-describedby={id} />
        </label>
      </div>
      <span id={id}>Make sure to include full name</span>
    </div>
  );
}
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67. Use the useSyncExternalStoreto subscribe to an external store

This is a rarely needed but super powerful hook 💪.

Use this hook if:

  • You have some state not accessible in the React tree (i.e., not present in the state or context)
  • The state can change, and you need your component to be notified of changes

In the example below, I want a Logger singleton to log errors, warnings, info, etc., in my entire app.

These are the requirements:

  • I need to be able to call this everywhere in my React app (even inside non-React components), so I won't put it inside a state/context.
  • I want to display all the logs to the user inside a Logs component

👉 I can use useSyncExternalStore inside my Logs component to access the logs and listen to changes.

function createLogger() {
  let logs = [];
  let listeners = [];

  const pushLog = (log) => {
    logs = [...logs, log];
    listeners.forEach((listener) => listener());
  };

  return {
    getLogs: () => Object.freeze(logs),
    subscribe: (listener) => {
      listeners.push(listener);
      return () => {
        listeners = listeners.filter((l) => l !== listener);
      };
    },
    info: (message) => {
      pushLog({ level: "info", message });
      console.info(message);
    },
    error: (message) => {
      pushLog({ level: "error", message });
      console.error(message);
    },
    warn: (message) => {
      pushLog({ level: "warn", message });
      console.warn(message);
    },
  };
}

export const Logger = createLogger();
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🏖 Sandbox

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68. Use the useDeferredValue hook to display the previous query results until the new results become available

Imagine you're building an app that represents countries on a map.

Users can filter to see countries up to a specific population size.

Every time maxPopulationSize updates, the map is re-rendered (see sandbox below).

🏖 Sandbox

As a result, notice how janky the slider is when you move it too fast. This is because the map is re-rendered every time the slider moves.

To solve this, we can use the useDeferredValue hook so that the slider updates smoothly.

<Map
    maxPopulationSize={deferredMaxPopulationSize}
    // …
/>
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If you're looking for another great usage, check out this post.

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Category #10: Must-known React Libraries/Tools 🧰

69. Incorporate routing into your app with react-router

If you need your app to support multiple pages, check out react-router.

You can find a minimal example here.

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70. Implement first-class data fetching in your app with swr or React Query

Data fetching can be notoriously tricky.

However, libraries like swr or React Query make it much easier.

I recommend swr for simple use cases and React Query for more complex ones.

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71. Simplify form state management with libraries like formik, React Hook Form, or TanStack Form

I used to hate form management in React 🥲.

That was until I discovered libraries like:

So make sure to check these out if you're struggling with forms.

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72. Internationalize your app using Format.js, Lingui, or react-i18next.

If your app needs to support multiple languages, it should be internationalized.

You can achieve this with libraries like:

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73. Effortlessly create impressive animations with framer-motion

Animations can make your app stand out 🔥.

You can create them easily with framer-motion.

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74. Tired of re-inventing the wheel with custom hooks? Check out https://usehooks.com/

If you're like me, you've written the same hooks over and over again.

So check usehooks.com first to see if someone has already done the work for you.

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75. Streamline app development by leveraging UI libraries like Shadcdn or Headless UI

It's hard to build UI at scale that is accessible, responsive, and beautiful.

Libraries like Shadcdn or Headless UI make it easier.

  • Shadcdn provides a set of accessible, reusable, and composable React components that you can copy and paste into your apps. At the time of writing, it requires Tailwind CSS.

  • Headless UI provides unstyled, fully accessible UI components that you can use to build your own UI components.

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76. Check your website's accessibility with the axe-core-npm library

Websites should be accessible to everyone.

However, it's easy to miss accessibility issues.

axe-core-npm is a fast, secure, and reliable way to check your website's accessibility while developing it.

💡 Tip: If you're a VSCode user, you can install the associated extension: axe Accessibility Linter.

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77. Refactor React code effortlessly with react-codemod

Codemods are transformations that run on your codebase programmatically 💻.

They make it easy to refactor your codebase.

For example, React codemods can help you remove all React imports from your codebase, update your code to use the latest React features, and more.

So, make sure to check those out before manually refactoring your code.

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78. Transform your app into a Progressive Web Application (PWA) using vite-pwa

Progressive Web Applications (PWAs) load like regular web pages but offer functionality such as working offline, push notifications, and device hardware access.

You can easily create a PWA in React using vite-pwa.

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Category #11: React & Visual Studio Code 🛠️

79. Enhance your productivity with the Simple React Snippets snippets extension

Bootstrapping a new React component can be tedious 😩.

Snippets from the Simple React Snippets extension make it easier.

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80. Set editor.stickyScroll.enabled to true to quickly locate the current component

I love this feature ❤️.

If you have a big file, it can be hard to locate the current component.

By setting editor.stickyScroll.enabled to true, the current component will always be at the top of the screen.

  • ❌ Without sticky scroll

Without Sticky Scroll

  • ✅ With sticky scroll

With Sticky Scroll

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81. Simplify refactoring with extensions like VSCode Glean or VSCode React Refactor

If you need to refactor your code frequently (for example, extract JSX into a new component), make sure to check out extensions like VSCode Glean or VSCode React Refactor.

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Category #12: React & TypeScript 🚀

82. Use ReactNode instead of JSX.Element | null | undefined | ... to keep your code more compact

I see this mistake a lot.

Instead of typing the leftElement and rightElement props like this:

const Panel = ({ leftElement, rightElement }: {
  leftElement:
    | JSX.Element
    | null
    | undefined
    // | ...;
  rightElement:
    | JSX.Element
    | null
    | undefined
    // | ...
}) => {
  //   …
};
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You can use ReactNode to keep the code more compact.

const MyComponent = ({ leftElement, rightElement }: { leftElement: ReactNode; rightElement: ReactNode }) => {
  //   …
};
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83. Simplify the typing of components expecting children props with PropsWithChildren

You don't have to type the children prop manually.

In fact, you can use PropsWithChildren to simplify the typings.

// 🟠 Ok
const HeaderPage = ({ children,...pageProps }: { children: ReactNode } & PageProps) => {
  //   …
};

// ✅ Better
const HeaderPage = ({ children, ...pageProps } : PropsWithChildren<PageProps>) => {
//   …
};
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84. Access element props efficiently with ComponentProps, ComponentPropsWithoutRef,…

There are cases where you need to figure out a component's props.

For example, let's say you want a button that will log to the console when clicked.

You can use ComponentProps to access the props of the button element then override the click prop.

const ButtonWithLogging = (props: ComponentProps<"button">) => {
  const handleClick: MouseEventHandler<HTMLButtonElement> = (e) => {
    console.log("Button clicked"); //TODO: Better logging
    props.onClick?.(e);
  };
  return <button {...props} onClick={handleClick} />;
};
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This trick also works with custom components.

const MyComponent = (props: { name: string }) => {
  //   …
};

const MyComponentWithLogging = (props: ComponentProps<typeof MyComponent>) => {
  //   …
};
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85. Leverage types like MouseEventHandler, FocusEventHandler and others for concise typings

Rather than typing the event handlers manually, you can use types like MouseEventHandler to keep the code more concise and readable.

// 🟠 Ok
const MyComponent = ({ onClick, onFocus, onChange }: {
  onClick: (e: MouseEvent<HTMLButtonElement>) => void;
  onFocus: (e: FocusEvent<HTMLButtonElement>) => void;
  onChange: (e: ChangeEvent<HTMLInputElement>) => void;
}) => {
  //   …
};

// ✅ Better
const MyComponent = ({ onClick, onFocus, onChange }: {
  onClick: MouseEventHandler<HTMLButtonElement>;
  onFocus: FocusEventHandler<HTMLButtonElement>;
  onChange: ChangeEventHandler<HTMLInputElement>;
}) => {
  //   …
};
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86. Specify types explicitly in useState, useRef, etc., when the type can't be or shouldn't be inferred from the initial value

Don't forget to specify the type when it can't be inferred from the initial value.

For example, in the example below, there is a selectedItemId stored in the state. It should be a string or undefined.

since the type is not specified, TypeScript will infer the type as undefined, which is not what we want.

// ❌ Bad: `selectedItemId` will be inferred as `undefined`
const [selectedItemId, setSelectedItemId] = useState(undefined);

// ✅ Good
const [selectedItemId, setSelectedItemId] = useState<string | undefined>(undefined);
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💡 Note: The opposite of this is that you don't need to specify the type when TypeScript can infer it for you.

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87. Leverage the Record type for cleaner and more extensible code

I love this helper type.

Let's say I have a type that represents log levels.

type LogLevel = "info" | "warn" | "error";
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We have a corresponding function for each log level that logs the message.

const logFunctions = {
  info: (message: string) => console.info(message),
  warn: (message: string) => console.warn(message),
  error: (message: string) => console.error(message),
};
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Instead of typing the logFunctions manually, you can use the Record type.

const logFunctions: Record<LogLevel, (message: string) => void> = {
  info: (message) => console.info(message),
  warn: (message) => console.warn(message),
  error: (message) => console.error(message),
};
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Using the Record type makes the code more concise and readable.

Additionally, it helps capture any error if a new log level is added or removed.

For example, if I decided to add a debug log level, TypeScript would throw an error.

Error with debug item

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88. Use the as const trick to accurately type your hook return values

Let's say we have a hook useIsHovered to detect whether a div element is hovered.

The hook returns a ref to use with the div element and a boolean indicating whether the div is hovered.

const useIsHovered = () => {
  const ref = useRef<HTMLDivElement>(null);
  const [isHovered, setIsHovered] = useState(false);
  // TODO : Rest of implementation
  return [ref, isHovered]
};
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Currently, TypeScript will not correctly infer the function return type.

Incorrect return type for function

You can either fix this by explicitly typing the return type like this:

const useIsHovered = (): [RefObject<HTMLDivElement>, boolean] => {
  // TODO : Rest of implementation
  return [ref, isHovered]
};
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Or you can use the as const trick to accurately type the return values:

const useIsHovered = () => {
  // TODO : Rest of implementation
  return [ref, isHovered] as const;
};
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89. Redux: Ensure proper typing by referring to https://react-redux.js.org/using-react-redux/usage-with-typescript to correctly type your Redux state and helpers

I love using Redux to manage heavy client-side state.

It also works well with TypeScript.

You can find a great guide on how to use Redux with TypeScript here.

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90. Simplify your types with ComponentType

Let's say you're designing an app like Figma (I know, you're ambitious 😅).

The app is made of widgets, each accepting a size.

To reuse logic, we can define a shared WidgetWrapper component that takes a widget of type Widget defined as follows:

interface Size {
  width: number;
  height: number
};

interface Widget {
  title: string;
  Component: ComponentType<{ size: Size }>;
}
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The WidgetWrapper component will render the widget and pass the relevant size to it.

const WidgetWrapper = ({ widget }: { widget: Widget }) => {
  const { Component, title } = widget;
  const { onClose, size, onResize } = useGetProps(); //TODO: better name but you get the idea 😅
  return (
    <Wrapper onClose={onClose} onResize={onResize}>
      <Title>{title}</Title>
      {/* We can render the component below with the size */}
      <Component size={size} />
    </Wrapper>
  );
};
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91. Make your code more reusable with TypeScript generics

If you're not using TypeScript generics, only two things could be happening:

  • You are either writing very simple code or,
  • You are missing out 😅

TypeScript generics make your code more reusable and flexible.

For example, let's say I have different items on a blog (e.g., Post, Follower, etc.), and I want a generic list component to display them.

export interface Post {
  id: string;
  title: string;
  contents: string;
  publicationDate: Date;
}

export interface User {
  username: string;
}

export interface Follower extends User {
  followingDate: Date;
}
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Each list should be sortable.

There is a bad and a good way to do this.

❌ Bad: I create a single list component that accepts a union of items.

This is bad because:

  • Every time a new item is added, the functions/types must be updated.
  • The function is not entirely type-safe (see This shouldn't happen comment).
  • This code depends on other files (e.g.: FollowerItem, PostItem).
  • Etc. 
import { FollowerItem } from "./FollowerItem";
import { PostItem } from "./PostItem";
import { Follower, Post } from "./types";

type ListItem = { type: "follower"; follower: Follower } | { type: "post"; post: Post };

function ListBad({
  items,
  title,
  vertical = true,
  ascending = true,
}: {
  title: string;
  items: ListItem[];
  vertical?: boolean;
  ascending?: boolean;
}) {
  const sortedItems = [...items].sort((a, b) => {
    const sign = ascending ? 1 : -1;
    return sign * compareItems(a, b);
  });

  return (
    <div>
      <h3 className="title">{title}</h3>
      <div className={`list ${vertical ? "vertical" : ""}`}>
        {sortedItems.map((item) => (
          <div key={getItemKey(item)}>{renderItem(item)}</div>
        ))}
      </div>
    </div>
  );
}

function compareItems(a: ListItem, b: ListItem) {
  if (a.type === "follower" && b.type === "follower") {
    return (
      a.follower.followingDate.getTime() - b.follower.followingDate.getTime()
    );
  } else if (a.type == "post" && b.type === "post") {
    return a.post.publicationDate.getTime() - b.post.publicationDate.getTime();
  } else {
    // This shouldn't happen
    return 0;
  }
}

function getItemKey(item: ListItem) {
  switch (item.type) {
    case "follower":
      return item.follower.username;
    case "post":
      return item.post.id;
  }
}

function renderItem(item: ListItem) {
  switch (item.type) {
    case "follower":
      return <FollowerItem follower={item.follower} />;
    case "post":
      return <PostItem post={item.post} />;
  }
}
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Instead, we can use TypeScript generics to create a more reusable and type-safe list component.

I made an example in the sandbox below 👇.

🏖 Sandbox

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92. Ensure precise typing with the NoInfer utility type

Imagine you're developing a video game 🎮.

The game has multiple locations (e.g., LeynTir, Forin, Karin, etc.).

You want to create a function that teleports the player to a new location.

function teleportPlayer<L extends string>(
  position: Position,
  locations: L[],
  defaultLocation: L,
) : L {
  // Teleport the player and return the location
}
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The function will be called this way:

const position = { x: 1, y: 2, z: 3 };
teleportPlayer(position, ["LeynTir", "Forin", "Karin"], "Forin");
teleportPlayer(position, ["LeynTir", "Karin"], "anythingCanGoHere"); // ❌ This will work, but it is wrong since "anythingCanGoHere" shouldn't be a valid location
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The second example is invalid because anythingCanGoHere is not a valid location.

However, TypeScript will not throw an error since it inferred the type of L from the list and the default location.

To fix this, use the NoInfer utility type.

function teleportPlayer<L extends string>(
  position: Position,
  locations: L[],
  defaultLocation: NoInfer<L>,
) : NoInfer<L> {
  // Teleport the player and return the location
}
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Now TypeScript will throw an error:

teleportPlayer(position, ["LeynTir", "Karin"], "anythingCanGoHere"); // ❌ Error: Argument of type '"anythingCanGoHere"' is not assignable to parameter of type '"LeynTir" | "Karin"
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Using the NoInfer utility type ensures that the default location must be one of the valid locations provided in the list, preventing invalid inputs.

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93. Effortlessly type refs with the ElementRef type helper

There is a hard and easy way to type refs.

The hard way is to remember the element's type name and use it directly 🤣.

const ref = useRef<HTMLDivElement>(null);
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The easy way is to use the ElementRef type helper. This method is more straightforward since you should already know the element's name.

const ref = useRef<ElementRef<"div">>(null);
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Category #13: Miscellaneous Tips 🎉

94. Boost your code's quality and safety with eslint-plugin-react and Prettier.

You can't be serious about React if you're not using eslint-plugin-react😅.

It helps you catch potential bugs and enforce best practices.

So, make sure to install and configure it for your project.

You can also use Prettier to format your code automatically and ensure your codebase is consistent.

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95. Log and monitor your app with tools like Sentry or Grafana Cloud Frontend Observability.

You can't improve what you don't measure 📏.

If you're looking for a monitoring tool for your production apps, check out Sentry or Grafana Cloud Frontend Observability.

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96. Start coding quickly with online IDEs like Code Sandbox or Stackblitz

Local development environments can be a pain to set up.

Especially as a beginner 🐣.

So start with online IDEs like Code Sandbox or Stackblitz.

These tools allow you to start coding quickly without worrying about setting up your environment.

Back to top ⬆️

97. Looking for advanced react skills? Check out these books 👇

If you're looking for advanced React books 📚, I would recommend:

Back to top ⬆️

98. Prepping React interviews? Check reactjs-interview-questions

React interviews ⚛️ can be tricky.

Luckily, you can prep for them by checking this repo.

Back to top ⬆️

99. Learn React best practices from experts like Nadia, Dan, Josh, Kent, etc.

If you want to stay up-to-date with the best practices and learn tips, make sure to follow experts like:

Back to top ⬆️

100. Stay updated with the React ecosystem by subscribing to newsletters like This Week In React or ui.dev

React is a fast-moving ecosystem.

There are many tools, libraries, and best practices to keep up with.

To stay updated, make sure to subscribe to newsletters 💌 like:

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101. Engage with the React community on platforms like r/reactjs

The React community is fantastic.

You can learn a lot from other developers and share your knowledge.

So engage with the community on platforms like r/reactjs.

That's a wrap 🎉.

Leave a comment 📩 to share your favorite tip (or add one).

And don't forget to drop a "💖🦄🔥".

If you're learning React, download my 101 React Tips & Tricks book for FREE.

If you like articles like this, join my FREE newsletter, FrontendJoy.

If you want daily tips, find me on X/Twitter.

Top comments (35)

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thethirdrace profile image
TheThirdRace •

Very great article. I agree this should definitely be a must-read for anyone working with React

I would like to point out a few improvements to the examples.

#8 - Use IIFE to keep your code clean and avoid lingering variables

I would strongly discourage the use of IIFE. It's too easy to miss while reading the code and you don't really get much benefits from them anymore.

Readability is better than performance unless performance is absolutely required. In my career, I've come across maybe 2 situations where performance needed to trump readability.

#35 - React Context: Introduce a Provider component when the value computation is not straightforward

While it's pretty nice to abstract the logic for a provider outside the actual component code, I believe your example shows the wrong abstraction. A custom hook (#63) would have been more appropriate here.

The problem with "self-contained context provider" components is they are harder to use in tests. We embed logic in the self-contained function that needs to be mocked for a lot of tests depending on the values in the context. It's easier to keep your context provider "raw" and then you can simply use the same context provider in your tests and pass whatever you want for values. Still some mocking, but so much simpler that way.

#37 Simplify state updates with useImmer or useImmerReducer

While I fully see how easier it is with these hooks, it also trains you to manipulate an object without thinking about immutability.

This is a huge crutch! I've seen many developers being completely lost once they had to actually code the real thing. They didn't understand whatever principle they were replacing with these libraries, and they made a huge mess in the code base.

These libraries also tend to complicate the typings of your objects unnecessarily. I still have nightmares with Redux and ImmerJs, the "cure" was worse than the "problem".

My advice would be to avoid these kinds of libraries like the plague. They will not serve you well in your career in the long term.

#45 - Memoize callbacks or values returned from utility hooks to avoid performance issues

The example is not the best. In this case, fetchData should have already been memoized before being passed to useLoadData. Doing it in the children is "wrong" as it will be much less efficient this way.

#66 - Generate unique IDs for accessibility attributes with the useId hook

Your example shows 2 HTML elements with the same id... (input/span)

I recommend calling useId() once and composing your id for different components, ex:

const inputId = `input-${id}`
const spanId = `span-${id}`
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Obviously, I wouldn't name them inputId and spanId, but for illustrative purpose this is fine...

#82 Use ReactNode instead of JSX.Element | null | undefined | ...

I agree 100% with the notion, but the example is not the best one.

This should be used like slots are used in web-components.

children is pretty much the exception and should always be used with PropsWithChildren instead. You did use it right after in #83

Conclusion

Overall, an amazing article, kudos!!!

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_ndeyefatoudiop profile image
Ndeye Fatou Diop • • Edited

Thanks for the comments @thethirdrace 😀.

8: The reason why I recommend IIFE is that I don't like it when there are variables polluting the component. Ideally, we can extract the logic into a function, but sometimes it is not the best if the logic takes so many arguments (and it is hard to find a name for the function 😅). My example is indeed too simple to show the problem, but I can see code like this inside a component.

  // ... First part of the component

  // startTime and endTime are just polluting the component scope
  const { startTime, endTime } = getEventTimes(eventData, schedule, timeframe);

  let duration;

  if (!startTime && !endTime) {
    duration = 0; // No time data available
  } else if (!startTime) {
    duration = endTime - schedule.start; // Use the schedule's start time
  } else if (!endTime) {
    duration = schedule.end - startTime; // Use the schedule's end time
  } else {
    duration = endTime - startTime; // Calculate based on both start and end times
  }
 // ... Rest of the component
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In these cases, I am ok with someone either using IIFE or extracting the logic into a function.

35 You are right. As pointed out, I am indeed using the hook 😅. Will change it to make it much clearer!

37 So I was actually thinking like you before. But recently, I have been using the redux toolkit, and damn, the experience is so much nicer. That is why I think they are still worth exploring.

45 I actually disagree here. When I write code, I want to make it super easy for consumers. And if we require every consumer to memoize the function passed, it won't work every time. That is why I am using a ref here to make sure my callback doesn't change while still using the correct value of the function when called

66 I am using a single ID because the ID is associated with a single element: the name

82 You are right. The example is not the best. Will change it :)

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thethirdrace profile image
TheThirdRace • • Edited

#8 - IIFE

It's more about the syntax that is really hard to pick up for developers, mistakes are too easy to make.

I've seen people do some IIFE in useEffect just because they needed an async function there. But that isn't immediately obvious, and you can easily fix it with a syntax like this:

function Grade() {
  const averageGrade = () => {
    let gradeSum = 0;
    let gradeCount = 0;
    grades.forEach((grade) => {
      gradeCount++;
      gradeSum += grade;
    });
    return gradeSum / gradeCount;
  };

  return <>{averageGrade()}</>;
}
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As you can see, the syntax is basically the same without the IIFE that is hard to catch. We define the function normally and call it right after. Same principle, less mistakes possibilities.

While it may look like those 2 methods are the very same and there's no difference, there are in fact many.

The way people read text (western style => top->down & left->right), the IIFE will require 2 parallel contexts to load into memory, the function itself and the executing context (()()). This increase cognitive load as they need to be loaded at the same time in parallel.

Comparatively, by separating in 2 sections, you load those 2 contexts sequentially. You can read the whole function without worries and then you see it's called. This is already much easier to contextualize in memory because these things happen sequentially.

But there's another advantage to loading context sequentially like this. If you just want to have an idea of what the component does, you can easily see there's a function definition and skip to the next "block" without checking how the function does its work. Sequential context loading allows you to skim the code very fast without caring much about the details. This is not possible with IIFE because you need to figure out what that first parenthesis really means before closing the function context.

I want also to point out that the spacing is important to really delimitate the function from the return section. For the same reason we use spacing between paragraphs and after punctuation, spacing is essential to separate concepts in code.

These are very subtle things to take into account, but on large scale it makes your system so much more accessible and easier to work with.

#37 - Immer

Redux toolkit doesn't require ImmerJS to work, it's an option you can use out of the box, but not a necessity.

But I do get where you're coming from. It's much easier to read your state if there's a minimum amount of code.

I would argue it comes with a few problems though...

First, as mentioned in my previous post, you start to use that method everywhere because you're so used to it. Unfortunately, not all systems are built with Immer so you start to put bugs in other apps that don't use it because your brain isn't trained to see these mistakes. For your brain, all you can see is correct syntax. And the reviewers will not necessarily pick up on that because they never imagine someone would just assign the state like that because you just don't do that in their system. It's an unwritten rule for most likely 99.9% of production systems out there... The result is a bug in production, and not an obvious debug session because the coder and the review don't see the bug since their brain trick them into thinking the line is correct...

Second, you lose context of your state. When you do not use Immer and rebuild the state from the ground up in your reducer, you always see the whole story. But when using Immer, you only see whatever changes without any context. This is potentially very dangerous because you might not take into account everything you should.

Third, if you really need Immer to clean up the code, then I would argue your piece of state is way too complicated. You should split it up or flatten it, there's too much cognitive load in that state.

I used to always mutate in-place until I got these nasty bugs that took hours to debug. Immer will fix it in your code, but not in your head. I would argue fixing the concept in your head is going to be much more important for you than fixing it for that particular line of code.

#45 Memoize

When I write code, I want to make it super easy for consumers. And if we require every consumer to memoize the function passed, it won't work every time.

You definitely want to make your code super easy for consumers, no argument there. But I think you misunderstood what I meant here. I meant that the fetchData needs to be stable to begin with.

Even if you memoize the value at the consumer level, if the parent doesn't have a stable reference, then the memoization in the consumer will re-run on render.

I see you used a ref to avoid the memoization re-run in the consumer. Don't get me wrong, this is a clever pattern, but it's just a band-aid. You are going to have to do this in every consumer now, and for the lifetime of the app, and all developers in your app will have to do the same, etc. The technical debt balloons very fast.

By having a stable reference in the parent, the problem is solved at 1 place. You won't have to add code anywhere else; you solved it once and no consumer needs to worry about it. Simplicity at its finest.

I would also argue that a re-render is not the end of the world either. You can squeeze every ounce of performance out of your code, but if your performance budget is not totally used at the end of the render cycle, it's thrown out. So any excess in performance you got might not be perceivable by users anyway. You prematurely optimized code that didn't even needed it, this is time that could have been spent elsewhere. We all should strive for performant apps, but at some point there are diminishing returns and it's our job to figure out when it's necessary and when it's not.

Also, this might not even be necessary at all now with the new React Compiler. The function will have a stable reference in the parent without requiring you to do anything about it. On the other hand, your pattern will still leave a lot of code in lots of consumers, which is less performant and less maintainable than no code at all.

#66 - ids

id should be unique by element, it has nothing to do with name. It's how the HTML syntax works.

The span and the input should not, at any point, have the same id. Browsers will let you do it just fine, but developers will have a hard time when querying by id.

You should not ignore this because we're in React here. It doesn't matter, it is a bug. That's why I pointed it out.

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_ndeyefatoudiop profile image
Ndeye Fatou Diop • • Edited

#8 *IIFE * — I see your point. I am used to the syntax so that is probably why I missed that it could be hard for new devs. I will adapt it! Thanks :)

#37 Immer— I see your point. However, I will still leave it as a tip since it can really make life easier. I will defer to people's judgment.

#45 Memoize — I am not following your reasoning. The whole point with this hook is that consumers don't have any memoization to do. I am aware that React Compiler is coming: which gives even more sense to not having memoization be done by consumers. Whether or not memoization is needed, everyone's codebase is different. I prefer to memoize hooks' returns values (like libraries do) from experience and given my situation, but obviously, everyone is free to memoize or not ;)

#66 ids — Oh sorry, I missed that. You are right: ids should always be unique. Replacing it!

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thethirdrace profile image
TheThirdRace •

#45 - Memoize

I am not following your reasoning. The whole point with this hook is that consumers don't have any memoization to do.

Ah I see, we simply are not focusing on the same thing😅

The problems with the example are manyfold.

1. The ref + useEffect is memoization with extra steps

If you simply wanted to memoize everything, you should do this:

function useLoadData(fetchData) {
  const [result, setResult] = useState({
    type: "notStarted",
  });

  const loadData = useCallback(async () => {
    setResult({ type: "loading" });
    try {
      const data = await fetchData();
      setResult({ type: "loaded", data });
    } catch (err) {
      setResult({ type: "error", error: err });
    }
  }, [fetchData, setResult]);

  return useMemo(() => ({ result, loadData }), [result, loadData])
}
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The useCallback dependency array solves all your requirements and is much simpler.

Instead, your "good" example replaced the standard dependency array method by 1 indirection (the ref) and 1 extra step for synchronization (the useEffect). Plus, now the value contained in fetchDataRef is not calculated at render, but at the useEffect phase so you added an asynchronous step to the state of your component.

You don't need the ref or the useEffect steps at all. The dependency array was enough to adjust the value without any extra step. As a bonus, the value is calculated at render and in a synchronous way.

Furthermore, the code is much simpler this way. You don't have to keep all these extra steps in your memory to understand how it works. The cognitive load is lower, and this makes it easier for people to understand the code.

2. fetchData is not memoized at all...

🚨 When you want to memoize a value, you need to do it when you define the variable that holds the value.

Given that fetchData is defined outside the hook, as it's passed by the consumer, memoizing it here doesn't have an impact on re-renders in the consumer.

If fetchData is defined in the consumer and you didn't memoize it at creation time, then it will be recalculated on every render of the consumer. What was the point in synchronizing the new function reference in useLoadData if you could have simply used the new function to begin with?

If fetchData came from the parent of the consumer, then any state change in the parent would re-render the consumer (because the consumer is a children of the parent).

Your memoization in the consumer itself didn't prevent a re-render of the consumer at all in this case. Again, what was the point in using all that extra code if it's going to be re-calculated anyway?

I would even ask what was the point of useMemo in useLoadData?

You need to execute the whole hook to know if 2 references have changed. If they did change, you are returning the 2 new references. If they didn't change, you are returning the 2 old references. In both case, you return 2 references, all the calculations have been done already and you memoized the tiniest and fastest possible data ever, so what did you save by adding so much code around it?

Don't get me wrong, I think your whole article is amazing. I'm simply pointing out that you might need to revisit the memoization concepts because there's a tiny gap there. And I cannot stress enough that you get it better than 99.99% of developers, even if you have a tiny gap missing.

This is also why most of the time it's better not to use memoization at all. It's a very easy concept to grasp, but it's a very hard one to apply correctly. And mistakes in applying it are worse than not applying it at all.

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_ndeyefatoudiop profile image
Ndeye Fatou Diop •

So, I still think there is a misunderstanding here. I am using a ref here instead of useCallback dependencies because I explicitly don't want my callback to change, which will be the case if I use a dependencies array (all items will need to be memoized).

Here, what I like in this pattern is that the entire complexity lives in this single hook.

Check similar implementations like in here or here for example.

Thread Thread
 
thethirdrace profile image
TheThirdRace •

I understand what you want to achieve, and I agree to a certain degree. If the hook didn't receive a parameter that is NOT memoized, I would be 100% behind the principle.

The flaw I'm pointing at is that the hook is getting a parameter that is not memoized. In turn, this has a few adverse effects...

One of them is that it's most likely slower to run the useEffect to synchronise the fetchDataRef than actually redeclaring the loadData function every render. Memoizing is supposed to be used for expansive compute, this is just a function declaration so there's no expansive compute.

Another adverse effect is you have complexified your code a lot. Developers now have to take into account the useCallback implications AND the useEffect synching. Your code would most likely be just as fast without any memoization at all and would be much simpler. The "bad" example is actually good because you didn't mesure what you saved; you did premature optimization without an ounce of evidence.

The worse adverse effect is the bug probability part. When reading a useCallback with an empty dependency array, most will take for granted that nothing can change the function. But this is not true because you can change the fetchData function and fetch something completely different between 2 calls. Making a wrong assumption here can lead to many bugs down the line. Your good intention is opening the door for many possible problems because you didn't use the standard dependency array. You can't expect developers to follow uncommon patterns without making mistakes.

Remember, any state update of the consumer component and all its hooks will re-render the consumer and all its children. The only way to stop a re-render down the chain is to either use {children} in the JSX or to use memo() on a component or function. Anything else needs to execute the function/component to know if they should or not apply changes to the DOM. What you saved in the "good" example is the reference pointer to the values, you're not memoizing the execution of any code here, which kind of defeat the point of the memoization in your example.

But at the end of the day, it's not the end of the world. I know I'm picking on a detail here, there are much worse things in the day to day code. I just hope that what I wrote and the "argument" we had will shed some light for people reading the article.

Thanks for your article and taking the time to explain more your ideas, it's really appreciated 👍

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albertocubeddu profile image
Alberto Cubeddu •

This article should be a must-read for anyone working with REACT!

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_ndeyefatoudiop profile image
Ndeye Fatou Diop •

So glad you like it Alberto ☺️

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77pintu profile image
77pintu •

Thank you for the fantastic post!

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_ndeyefatoudiop profile image
Ndeye Fatou Diop •

Thanks 🙏

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jakubgarfield profile image
Jakub Chodounsky •

Neat article! I'll run it in the next issue of React Digest. Perhaps consider including in #100 if you'd like it. 😉

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_ndeyefatoudiop profile image
Ndeye Fatou Diop •

Wouaw thanks a lot Jakub. I would love it 😻

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nawael profile image
Nawael •

A very impressive article!

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_ndeyefatoudiop profile image
Ndeye Fatou Diop •

Thanks Nawael 🙏

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cfecherolle profile image
Cécile Fécherolle •

Amazing article, very thorough. Kudos 👏

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_ndeyefatoudiop profile image
Ndeye Fatou Diop •

Thanks Cecile

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geesman profile image
Kenneth •

Nice piece

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_ndeyefatoudiop profile image
Ndeye Fatou Diop •

Thanks!

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franio68 profile image
franio68 •

Great!! Mega-helpful. Thanks

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_ndeyefatoudiop profile image
Ndeye Fatou Diop •

So glad you like it ☺️

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thanupakon_chinnaket_1200 profile image
Thanupakon Chinnaket •

Thank you very much. This article is very useful.

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_ndeyefatoudiop profile image
Ndeye Fatou Diop •

Super glad you like it 🙌

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getsetgopi profile image
GP •

Thanks for taking time to put together the best practices and standards. This link will definitely go into our confluence page.

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_ndeyefatoudiop profile image
Ndeye Fatou Diop •

Thanks a lot GP!
Super glad you like it 🙏

View full discussion (35 comments)

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