React.js interview questions with answers Part-1

1.What are React hooks?

Ans: React Hooks are functions that allow functional components in React to have state, lifecycle methods, and other functionality that was previously only available to class components.

1. Explain the useEffect hook ?

Ans: useEffect is a hook to perform side effects in functional components. It runs on every render and can be used to fetch data, subscribe, manually modify the DOM etc.

1. What is the useState hook ?

Ans: The useState hook in React is used to add state variables to functional components so that they can track state changes and trigger re-renders.

1. What is the purpose of useReducer hook ?

Ans: useReducer is a hook in React used for state management. It is suitable for managing complex state logic with multiple sub-values or when the next status depends on the previous status.

1. What is the purpose of useCallback hook in React ?

Ans: useCallback is used to store callback functions and prevent unnecessary re-rendering of child components that depend on these callbacks.

1. Explain the concept of Hook rules in React ?

Ans: The rules for using Hooks in React include that they are called at the top level, they are called only from function components or custom Hooks, and they follow a naming convention. For example- starting with “use”.

1. What is the purpose of useMemo hook in React ?

Ans: useMemo hook is used to store the results of calculations. It helps in performance optimization by preventing unnecessary recalculations.

1. What is the importance of useRef hook in React ?

Ans: useRef is used to create mutable object properties that persist across multiple renders without re-rendering when a change occurs. It is often used to access and change properties of DOM elements.

1. What is PureComponent in React ?

Ans: PureComponent is a base class for class components that implements the shouldComponentUpdate method to do superficial property and state comparisons. This helps prevent unnecessary rendering for performance optimization.

1. What are React Fragments ?

Ans: React Fragments allow you to group multiple elements together without adding unnecessary nodes to the DOM. This is useful when you don’t want to introduce an additional parent div.

1. What is the importance of keys in React lists ?

Ans: Keys are used to help React detect which items in the list have changed, added, or removed. They help optimize the rendering process.

1. What is React’s Context API ?

Ans: The Context API provides a way to pass data through a component tree without having to manually pass props at each level.

1. How does React Prop handle drilling ?

Ans: Prop drilling occurs when you route a prop to multiple component levels. The solution is to use Context API or Redux for global state management.

1. What is the importance of keys in React lists ?

Ans: Keys are used to help React detect which items in the list have been changed, added, or removed. They help in optimizing the rendering process.

1. Explain the concept of lazy loading in React ?

Ans: Lazy loading is a technique where a component or resource is loaded only when it is actually required. React provides the React.lazy feature to lazily load components.