In React, what is the component lifecycle?


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In React, the life cycle of a component refers to the entire process from creation to destruction of the component. React provides some specific methods that allow you to execute code at different moments. These methods are called lifecycle methods, and they allow you to perform specific actions at different stages of your component. Before React 16.3, the life cycle method could be divided into three stages: mount, update and uninstall. Starting with React 16.3, some lifecycle methods are marked as deprecated and new lifecycle methods are introduced. Here are the lifecycle methods in React and when they are called:


⭐Mounting phase (Mounting)

  1. constructor(): This is the component's constructor, called when the component is created. Typically, this is where you would initialize the component's state.

  2. static getDerivedStateFromProps(props, state): Called when the component is instantiated and when new props are received. Used to compute and return a new state object, or return nullwith the state unchanged.

  3. render(): Rendering method, used to return the virtual DOM structure of the component. This is the only required lifecycle method.

  4. componentDidMount(): Called immediately after the component is mounted to the DOM. Typically, this is where you perform side-effect operations such as data retrieval, subscribing to events, etc.


⭐Updating phase (Updating)

  1. static getDerivedStateFromProps(props, state): It can also be called during the update phase to respond to new props. Same as the mount phase.

  2. shouldComponentUpdate(nextProps, nextState): Called after the component receives new props or state, used to control whether to re-render the component. Return truemeans re-rendering, return falsemeans not re-rendering, the default is true.

  3. render(): Same as the mount phase, it will also be called during the update phase.

  4. getSnapshotBeforeUpdate(prevProps, prevState): called before actual rendering (before DOM update), can be used to capture the current DOM state (such as scroll position) and componentDidUpdateuse it in.

  5. componentDidUpdate(prevProps, prevState, snapshot): Called immediately after the component is updated. Typically this is where you perform operations or side effects that interact with the DOM.


⭐ Unmounting phase (Unmounting)

  1. componentWillUnmount(): Called when the component is about to be unmounted from the DOM. Typically this is where you would unsubscribe from events, clean up timers, and other resource release operations.

⭐ Error Handling

  1. static getDerivedStateFromError(error): Called after the child component throws an error, used to update the state to display the error UI.

  2. componentDidCatch(error, info): Called after a child component throws an error, used to record error information or report errors.


⭐ New lifecycle methods

Starting with React version 16.3, some new lifecycle methods are introduced, mainly to replace obsolete methods and enhance functionality. These new methods include getDerivedStateFromPropsand getSnapshotBeforeUpdateet al.

It should be noted that obsolete life cycle methods (such as componentWillMount, componentWillReceivePropsetc.) may be removed in future versions, so it is recommended to use new life cycle methods as much as possible.

Understanding the lifecycle methods of React components helps you better manage the behavior and side effects of components to meet different needs.


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