What are hooks in React js?

Hooks in React.js are functions that enable functional components to use state and other React features without writing a class.

Prior to the introduction of hooks in React 16.8, state and other component features were only available in class components. Hooks provide a way to use state and side-effects in functional components, making them more powerful and versatile.

In React.js, hooks are functions that enable functional components to use state and other React features without writing a class. They were introduced in React version 16.8 to address complex state management and reusability issues in functional components.

The most commonly used hooks include:

1. useState: This hook used for managing state within functional components. It enables the creation of state variables and provides a method for updating them.

2. useEffect: This hook allows performing side effects in functional components. It runs after every render and replaces lifecycle methods like componentDidMount, componentDidUpdate, and componentWillUnmount.

3. useContext: This hook is a built-in hook that allows functional components to consume values from the Context API. The Context API provides a way to share values, such as global state, between components without passing props through every level of the component tree manually.

4. useReducer: This hook provides an alternative to useState for managing state in functional components. It is used for managing more complex state logic where the next state depends on the previous one and involves multiple sub-values. useReducer takes a reducer function and an initial state, returning the current state and a dispatch function to update the state based on actions dispatched to the reducer. This hook is particularly useful for managing state in components with intricate state transitions or logic.

5. useCallback: This hook returns a memoized callback function. It is useful when passing callbacks to optimized child components that rely on reference equality to prevent unnecessary renders.

6. useMemo: This hook returns a memoized value. It is useful for optimizing performance by memoizing expensive calculations.

7. useRef: This hook returns a mutable ref object whose .current property is initialized to the passed argument (initialValue). It allows you to persist values across renders without causing re-renders.

8. useLayoutEffect: This hook is similar to useEffect but fires synchronously after all DOM mutations. It is useful for measuring the size or position of DOM elements.

Hooks enable developers to write cleaner, more concise code by encapsulating logic and state management within functional components. They promote code reusability and make it easier to reason about the behavior of components.