The life cycle of the React component is divided into three stages: mount, update and uninstall. Each stage has a corresponding life cycle hook function. 1. The mount phase includes constructor() for initializing state, render() returns JSX content, componentDidMount() is suitable for initiating data requests or setting timers. 2. The update phase includes render() to re-render the UI. componentDidUpdate(prevProps, prevState) is used to handle side effects operations, such as obtaining new data according to state changes. 3. The uninstallation phase is componentWillUnmount(), which is used to clean up timers, unsubscribe and other operations. Common errors include asynchronous requests in componentWillMount, side effects not being cleaned up in componentWillUnmount, and modifying state in render causes loop updates. Mastering the characteristics of each stage can effectively improve the performance and stability of React applications.

The React component life cycle refers to the entire process of a component from creation, rendering, updating, and finally uninstalling. During this process, React automatically calls certain methods, which are called "Lifecycle Hooks". They allow you to execute custom logic at different stages of a component, such as loading data, cleaning up resources, or responding to state changes.

Understanding the life cycle is very important for writing efficient and stable React applications. Especially in class components, life cycle hooks are particularly critical. Let’s take a look at several common life cycle stages and corresponding commonly used hook functions.

1. Component Mounting

This is the process that occurs when the component is first added to the DOM. At this stage, React will call the following methods in turn:

• constructor() : Where to initialize state and binding methods.
• render() : A method that must be implemented to return JSX content.
• componentDidMount() : Called after the component is mounted, suitable for data requests or timers setting and other operations.

For example, initiate an API request in componentDidMount , obtain the initial data and update the state:

 componentDidMount() {
fetch('/api/data')
.then(res => res.json())
.then(data => this.setState({ items: data }));
}

2. Component update phase (Updating)

When the component's props or state changes, it will enter the update phase. This stage mainly involves the following hooks:

• render() : Re-render the UI.
• componentDidUpdate(prevProps, prevState) : Called after the update is completed, suitable for side effects operations based on new props or state.

For example, you just want to execute some logic after a specific state change:

 componentDidUpdate(prevProps, prevState) {
if (prevState.selectedId !== this.state.selectedId) {
this.fetchDetails(this.state.selectedId);
}
}

3. Component uninstallation stage (Unmounting)

When the component is moved out of the DOM, React will call:

• componentWillUnmount() : You can do some cleaning work here, such as clearing timers, unsubscribe events, etc.

For example, if you set a timer in componentDidMount , remember to clear it here:

 componentWillUnmount() {
clearInterval(this.timer);
}

4. Common Errors and Precautions

Some newbies may perform actions during the wrong lifecycle phase, causing problems. for example:

• Initiate an asynchronous request in componentWillMount : it is deprecated and may result in duplicate requests.
• Forgot to clean up side effects in componentWillUnmount : easy to cause memory leaks.
• Modifying state in render : will cause an infinite loop.

Basically that's it. Although the life cycle of React components seems a bit too many, as long as you master the characteristics and applicable scenarios of each stage, you can control the behavior of components more freely.

The above is the detailed content of What is React component lifecycle. For more information, please follow other related articles on the PHP Chinese website!