Understand React.js Components Lifecycle.

In React class components, there is a sequence of lifecycle methods that are invoked during the creation and destruction of components. These methods enable developers to execute specific code at different stages of a component's life. As of React 16.3, some of these methods are considered legacy and may not be used in future versions. Here's an overview of the React component lifecycle methods:

 Mounting Lifecycle Methods:

1. constructor(props): This method is the component's constructor and is called before the component is mounted. It is used to initialize state and bind event handlers.

2. static getDerivedStateFromProps(props, state): This method is called just before rendering when new props or state are received. It returns an object to update the state or `null` if no state update is needed.

3. render(): The `render` method is essential and returns React elements to be rendered in the DOM. It is a pure function without side-effects.

4. componentDidMount(): This method is invoked after the component is rendered to the DOM. It is suitable for initiating network requests or setting up subscriptions.

 Updating Lifecycle Methods:

1. static getDerivedStateFromProps(props, state): This method is also called during the updating phase, similar to the mounting phase. It can be used for both mounting and updating scenarios.

2. shouldComponentUpdate(nextProps, nextState): This method is called before rendering when new props or state are received. It determines whether the component should re-render, returning `true` if it should, and `false` otherwise (default is `true`).

3. render(): The `render` method is called again to update the DOM in response to state or prop changes.

4. getSnapshotBeforeUpdate(prevProps, prevState): This method is invoked just before changes from the DOM are reflected in the component. It allows the component to capture some information from the DOM before potential changes.

5. componentDidUpdate(prevProps, prevState, snapshot): This method is called after the component is updated in the DOM. It is suitable for performing network requests, given that you compare the current props to the previous props.

 Unmounting Lifecycle Method:

1. componentWillUnmount(): This method is called immediately before a component is unmounted and destroyed. It's used for cleanup tasks like unsubscribing from subscriptions or clearing timers.

Error Handling Lifecycle Methods (introduced in React 16):

1. static getDerivedStateFromError(error): This method is used to render a fallback UI after an error is thrown in a descendant component. It receives an error as a parameter and returns an object to update the state.

2. componentDidCatch(error, info): This method is called after an error has been thrown by a descendant component. It receives `error` (the thrown error) and `info` (an object with a `componentStack` key containing information about which component threw the error).

With the advent of React hooks, functional components can now utilize hooks like `useState` and `useEffect` to achieve similar functionality, making traditional component lifecycle methods less necessary for many use cases. Hooks offer a more concise and readable way to manage state and side effects in functional components.