Understanding React Lifecycle Methods in Class Components

When working with React, components have a life cycle that consists of different phases. Lifecycle methods are special functions that allow you to run code at specific points during a component's creation, update, and removal. Here’s a breakdown of these lifecycle stages:

1. Mounting Phase (When the Component is Added to the DOM)

- constructor(props)
This is called first when a component is created. It’s used to initialize state and bind methods.

- static getDerivedStateFromProps(props, state) (rarely used)
Updates the state based on changes in props before rendering.

- render()
Describes what to display in the UI. It must be pure and cannot cause side effects.

- componentDidMount()
Runs after the component has been inserted into the DOM. It’s commonly used for API calls, subscriptions, or starting timers.

---

2. Updating Phase (When Props or State Change)

- static getDerivedStateFromProps(props, state) (rarely used)
Executes before every re-render, allowing state updates based on new props.

- shouldComponentUpdate(nextProps, nextState) (optional)
Controls whether the component should re-render. Useful for performance optimization.

- render()
Called again to update the UI.

- getSnapshotBeforeUpdate(prevProps, prevState) (rarely used)
Captures information (like scroll position) from the DOM before it changes.

- componentDidUpdate(prevProps, prevState)
Runs after the component updates. Ideal for additional API calls or DOM manipulations.

---

3. Unmounting Phase (When the Component is Removed)

- componentWillUnmount()
Called right before the component is destroyed. Perfect for cleanup tasks like removing event listeners, canceling API calls, or clearing timers.

---

Lifecycle Flow Overview

Hooks Equivalent in Functional Components

With the introduction of Hooks, functional components can mimic these lifecycle behaviors:

• componentDidMount → useEffect(() => {...}, [])
• componentDidUpdate → useEffect(() => {...}, [dependencies])
• componentWillUnmount → Cleanup function inside useEffect

Understanding these lifecycle methods is crucial for building robust and optimized React applications. Whether you use class components or modern functional components with hooks, knowing when and how components render and update is essential for effective development.