React Style Guide (2021)

src: the original post: https://github.com/airbnb/javascript/tree/master/react

I wanted to create this post to mark back what's important when someone is just starting out with React. Therefore, I would like to receive comments from everyone.

Basic Rules

• Only include one React component per file.
• Always use JSX syntax.

Naming

• List itemExtensions: Use .jsx extension for React components. eslint: react/jsx-filename-extension
• Filename: Use PascalCase for filenames. E.g., ReservationCard.jsx.
• Reference Naming: Use PascalCase for React components and camelCase for their instances.

// bad
import reservationCard from './ReservationCard';

// good
import ReservationCard from './ReservationCard';

// bad
const ReservationItem = <ReservationCard />;

// good
const reservationItem = <ReservationCard />;

• Component Naming: Use the filename as the component name. For example, ReservationCard.jsx should have a reference name of ReservationCard. However, for root components of a directory, use index.jsx as the filename and use the directory name as the component name:

// bad
import Footer from './Footer/Footer';

// bad
import Footer from './Footer/index';

// good
import Footer from './Footer';

• Higher-order Component Naming: Use a composite of the higher-order component’s name and the passed-in component’s name as the displayName on the generated component. For example, the higher-order component withFoo(), when passed a component Bar should produce a component with a displayName of withFoo(Bar).

  Why? A component’s displayName may be used by developer tools or in error messages, and having a value that clearly expresses this relationship helps people understand what is happening.
  

  // bad
  export default function withFoo(WrappedComponent) {
    return function WithFoo(props) {
      return <WrappedComponent {...props} foo />;
    }
  }
  
  // good
  export default function withFoo(WrappedComponent) {
    function WithFoo(props) {
      return <WrappedComponent {...props} foo />;
    }
  
    const wrappedComponentName = WrappedComponent.displayName
      || WrappedComponent.name
      || 'Component';
  
    WithFoo.displayName = `withFoo(${wrappedComponentName})`;
    return WithFoo;
  }
  

Declaration

• Do not use displayName for naming components. Instead, name the component by reference.
  

  // bad
  export default React.createClass({
    displayName: 'ReservationCard',
    // stuff goes here
  });
  
  // good
  export default function ReservationCard(props) {
      return ()
  }
  

Alignment

• Follow these alignment styles for JSX syntax. eslint: react/jsx-closing-bracket-location react/jsx-closing-tag-location
  

  // bad
  <Foo superLongParam="bar"
       anotherSuperLongParam="baz" />
  
  // good
  <Foo
    superLongParam="bar"
    anotherSuperLongParam="baz"
  />
  
  // if props fit in one line then keep it on the same line
  <Foo bar="bar" />
  
  // children get indented normally
  <Foo
    superLongParam="bar"
    anotherSuperLongParam="baz"
  >
    <Quux />
  </Foo>
  
  // bad
  {showButton &&
    <Button />
  }
  
  // bad
  {
    showButton &&
      <Button />
  }
  
  // good
  {showButton && (
    <Button />
  )}
  
  // good
  {showButton && <Button />}
  
  // good
  {someReallyLongConditional
    && anotherLongConditional
    && (
      <Foo
        superLongParam="bar"
        anotherSuperLongParam="baz"
      />
    )
  }
  
  // good
  {someConditional ? (
    <Foo />
  ) : (
    <Foo
      superLongParam="bar"
      anotherSuperLongParam="baz"
    />
  )}
  

Props

• Always use camelCase for prop names, or PascalCase if the prop value is a React component.
  

  // bad
  <Foo
    UserName="hello"
    phone_number={12345678}
  />
  
  // good
  <Foo
    userName="hello"
    phoneNumber={12345678}
    Component={SomeComponent}
  />
  

• Omit the value of the prop when it is explicitly true. eslint: react/jsx-boolean-value
  

  // bad
  <Foo
    hidden={true}
  />
  
  // good
  <Foo
    hidden
  />
  
  // very good
  <Foo hidden />
  

• Avoid using an array index as key prop, prefer a stable ID. eslint: react/no-array-index-key

Why? Not using a stable ID is an anti-pattern because it can negatively impact performance and cause issues with component state.

We don’t recommend using indexes for keys if the order of items may change.

  // bad
  {todos.map((todo, index) =>
    <Todo
      {...todo}
      key={index}
    />
  )}

  // good
  {todos.map(todo => (
    <Todo
      {...todo}
      key={todo.id}
    />
  ))}

• Always define explicit defaultProps for all non-required props.

Why? propTypes are a form of documentation, and providing defaultProps means the reader of your code doesn’t have to assume as much. In addition, it can mean that your code can omit certain type checks.

  // bad
  function SFC({ foo, bar, children }) {
    return <div>{foo}{bar}{children}</div>;
  }
  SFC.propTypes = {
    foo: PropTypes.number.isRequired,
    bar: PropTypes.string,
    children: PropTypes.node,
  };

  // good
  function SFC({ foo, bar, children }) {
    return <div>{foo}{bar}{children}</div>;
  }
  SFC.propTypes = {
    foo: PropTypes.number.isRequired,
    bar: PropTypes.string,
    children: PropTypes.node,
  };
  SFC.defaultProps = {
    bar: '',
    children: null,
  };

• Use spread props sparingly. > Why? Otherwise you’re more likely to pass unnecessary props down to components. And for React v15.6.1 and older, you could pass invalid HTML attributes to the DOM.

Exceptions:

• HOCs that proxy down props and hoist propTypes

  function HOC(WrappedComponent) {
    return class Proxy extends React.Component {
      Proxy.propTypes = {
        text: PropTypes.string,
        isLoading: PropTypes.bool
      };

      render() {
        return <WrappedComponent {...this.props} />
      }
    }
  }

• Spreading objects with known, explicit props. This can be particularly useful when testing React components with Mocha’s beforeEach construct.

  export default function Foo {
    const props = {
      text: '',
      isPublished: false
    }

    return (<div {...props} />);
  }

Notes for use:
Filter out unnecessary props when possible. Also, use prop-types-exact to help prevent bugs.

  // bad
  render() {
    const { irrelevantProp, ...relevantProps } = this.props;
    return <WrappedComponent {...this.props} />
  }

  // good
  render() {
    const { irrelevantProp, ...relevantProps } = this.props;
    return <WrappedComponent {...relevantProps} />
  }

Refs

• Always use ref callbacks. eslint: react/no-string-refs
  

  // bad
  <Foo
    ref="myRef"
  />
  
  // good
  <Foo
    ref={(ref) => { this.myRef = ref; }}
  />
  

Parentheses

• Wrap JSX tags in parentheses when they span more than one line. eslint: react/jsx-wrap-multilines
  

  // bad
  render() {
    return <MyComponent variant="long body" foo="bar">
             <MyChild />
           </MyComponent>;
  }
  
  // good
  render() {
    return (
      <MyComponent variant="long body" foo="bar">
        <MyChild />
      </MyComponent>
    );
  }
  
  // good, when single line
  render() {
    const body = <div>hello</div>;
    return <MyComponent>{body}</MyComponent>;
  }
  

Methods

• Use arrow functions to close over local variables. It is handy when you need to pass additional data to an event handler. Although, make sure they do not massively hurt performance, in particular when passed to custom components that might be PureComponents, because they will trigger a possibly needless rerender every time.
  

  function ItemList(props) {
    return (
      <ul>
        {props.items.map((item, index) => (
          <Item
            key={item.key}
            onClick={(event) => { doSomethingWith(event, item.name, index); }}
          />
        ))}
      </ul>
    );
  }
  

• Bind event handlers for the render method in the constructor. eslint: react/jsx-no-bind

  Why? A bind call in the render path creates a brand new function on every single render. Do not use arrow functions in class fields, because it makes them challenging to test and debug, and can negatively impact performance, and because conceptually, class fields are for data, not logic.
  

  // bad
  class extends React.Component {
    onClickDiv() {
      // do stuff
    }
  
    render() {
      return <div onClick={this.onClickDiv.bind(this)} />;
    }
  }
  
  // very bad
  class extends React.Component {
    onClickDiv = () => {
      // do stuff
    }
  
    render() {
      return <div onClick={this.onClickDiv} />
    }
  }
  
  // good
  class extends React.Component {
    constructor(props) {
      super(props);
  
      this.onClickDiv = this.onClickDiv.bind(this);
    }
  
    onClickDiv() {
      // do stuff
    }
  
    render() {
      return <div onClick={this.onClickDiv} />;
    }
  }
  

• Do not use underscore prefix for internal methods of a React component.

  Why? Underscore prefixes are sometimes used as a convention in other languages to denote privacy. But, unlike those languages, there is no native support for privacy in JavaScript, everything is public. Regardless of your intentions, adding underscore prefixes to your properties does not actually make them private, and any property (underscore-prefixed or not) should be treated as being public. See issues #1024, and #490 for a more in-depth discussion.
  

  // bad
  React.createClass({
    _onClickSubmit() {
      // do stuff
    },
  
    // other stuff
  });
  
  // good
  class extends React.Component {
    onClickSubmit() {
      // do stuff
    }
  
    // other stuff
  }
  

• Be sure to return a value in your render methods. eslint: react/require-render-return
  

  // bad
  render() {
    (<div />);
  }
  
  // good
  render() {
    return (<div />);
  }