ReactJS Tutorial - 24 - Component Updating Lifecycle Methods

Updating Life Cycle Methods in React

Overview of Updating Life Cycle Methods

• The video discusses the updating life cycle methods in React, which are invoked when a component is prerendered due to changes in props or state. There are five methods, three of which are rarely used.

Key Updating Life Cycle Methods

1. getDerivedStateFromProps

• This static method receives props and state as parameters and must return either null or an object representing the updated state. It is called every time a component rerenders and is useful when state depends on props. However, it should not cause side effects.

2. shouldComponentUpdate

• This method determines whether a component should rerender by comparing current and next props/state values. By default, components rerender with any prop/state change; this method can prevent that by returning false, optimizing performance without causing side effects.

3. render

• The familiar render method reads from this.props and this.state, returning JSX that describes the UI. It’s important to avoid changing state or interacting with the DOM within this method to maintain proper rendering behavior.

4. getSnapshotBeforeUpdate

• Accepting previous props and state as parameters, this method is called just before changes from the virtual DOM are reflected in the actual DOM. It captures information like scroll position for maintaining user experience post-update, returning either a value or null for further processing in subsequent lifecycle methods.

5. componentDidUpdate

• Called after rendering completes during rerender cycles, this method accepts previous props/state and snapshot values returned from getSnapshotBeforeUpdate. It's suitable for making AJAX calls based on comparisons between previous and current props to avoid unnecessary requests, ensuring efficient data fetching post-update actions occur only when needed.

Demonstration of Lifecycle Method Execution Order

• The presenter demonstrates adding these lifecycle methods into two components (lifecycle A & B) while logging their execution order upon triggering updates through state changes via button clicks in JSX code snippets provided during the demonstration phase of the video session.

Implementation Steps:

• Adding lifecycle methods sequentially:

• Start with getDerivedStateFromProps.

• Follow with shouldComponentUpdate.

• Include existing render logic.

• Add getSnapshotBeforeUpdate.

• Finally implement componentDidUpdate.

This setup allows observing how each lifecycle method executes during updates triggered by changing states through user interactions such as button clicks on screen elements defined within JSX code blocks presented throughout the demo section of the video content.

Understanding Component Lifecycle Methods in React

The Updating Phase of a Component

• The updating phase begins with the snapshot before update and component did update methods. In this sequence, the child component's method is executed first, followed by the parent component's method.

• It's emphasized that while render and component did update are commonly used during updates, the remaining three lifecycle methods should be utilized sparingly and only when necessary.

Mounting and Unmounting Phases

• The unmounting phase includes one critical method: component will unmount. This method is called right before a component is removed from the DOM, allowing for cleanup tasks such as canceling network requests or removing event handlers.

• It’s crucial not to call setState within component will unmount, as the component will no longer exist after this point. Proper cleanup ensures efficient resource management.

Error Handling Phase

• The error handling phase consists of two methods: static getDerivedStateFromError and componentDidCatch. These methods are invoked when an error occurs during rendering or in lifecycle methods of any child components.

• A deeper discussion on these error handling methods will occur later when exploring "error boundaries" in React, highlighting their importance in managing errors effectively within applications.