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React

286Class Component Structure: extends React.Component
287The render() Method: Class Components' Return
288this.props: Accessing Props in Classes
289this.state: The Class Component State Object
290constructor() and super(props)
291this.setState(): The Class Update API
292Binding Event Handlers: The this Problem
293Class Fields Syntax: Public Properties
294Static Properties: defaultProps and propTypes
295When You'll See Classes: Legacy Codebases and Error Boundaries
296The Three Lifecycle Phases: Mount, Update, Unmount
297componentDidMount: Side Effects After First Render
298componentDidUpdate: Responding to Props or State Changes
299componentWillUnmount: Cleanup Before Removal
300shouldComponentUpdate: Manual Render Optimization
301componentDidCatch and getDerivedStateFromError
302getDerivedStateFromProps: Syncing State to Props
303getSnapshotBeforeUpdate: Reading DOM Before Update
304The Deprecated Lifecycles: UNSAFE_ Prefix
305Common Lifecycle Patterns: Fetch on Mount
306Common Lifecycle Pitfalls: setState in componentDidUpdate
307The Lifecycle Diagram: Mental Model
308The 'this' Binding Problem
309Wrapper Hell and HOCs
310Giant Components and Related Logic Scattered
311Classes Confuse Both People and Machines
312No Way to Subscribe to Multiple Sources Cleanly
313Hooks Enable Logic Extraction
314Hooks Colocate Related Code
315The Mental Model Shift
316From constructor State to useState
317From componentDidMount to useEffect
318From componentDidUpdate to useEffect with Deps
319From componentWillUnmount to Effect Cleanup
320From this.setState to State Setters
321From Instance Variables to useRef
322From Render Props Pattern to Custom Hooks
323Error Boundaries: The Only Class-Exclusive Feature
324Legacy Codebases: Reading Old React Code
325Third-Party Libraries with Class APIs
326Documentation and Tutorials: Recognizing Outdated Content
327When Teams Haven't Migrated Yet
328Should You Write New Class Components?

React

286Class Component Structure: extends React.Component
287The render() Method: Class Components' Return
288this.props: Accessing Props in Classes
289this.state: The Class Component State Object
290constructor() and super(props)
291this.setState(): The Class Update API
292Binding Event Handlers: The this Problem
293Class Fields Syntax: Public Properties
294Static Properties: defaultProps and propTypes
295When You'll See Classes: Legacy Codebases and Error Boundaries
296The Three Lifecycle Phases: Mount, Update, Unmount
297componentDidMount: Side Effects After First Render
298componentDidUpdate: Responding to Props or State Changes
299componentWillUnmount: Cleanup Before Removal
300shouldComponentUpdate: Manual Render Optimization
301componentDidCatch and getDerivedStateFromError
302getDerivedStateFromProps: Syncing State to Props
303getSnapshotBeforeUpdate: Reading DOM Before Update
304The Deprecated Lifecycles: UNSAFE_ Prefix
305Common Lifecycle Patterns: Fetch on Mount
306Common Lifecycle Pitfalls: setState in componentDidUpdate
307The Lifecycle Diagram: Mental Model
308The 'this' Binding Problem
309Wrapper Hell and HOCs
310Giant Components and Related Logic Scattered
311Classes Confuse Both People and Machines
312No Way to Subscribe to Multiple Sources Cleanly
313Hooks Enable Logic Extraction
314Hooks Colocate Related Code
315The Mental Model Shift
316From constructor State to useState
317From componentDidMount to useEffect
318From componentDidUpdate to useEffect with Deps
319From componentWillUnmount to Effect Cleanup
320From this.setState to State Setters
321From Instance Variables to useRef
322From Render Props Pattern to Custom Hooks
323Error Boundaries: The Only Class-Exclusive Feature
324Legacy Codebases: Reading Old React Code
325Third-Party Libraries with Class APIs
326Documentation and Tutorials: Recognizing Outdated Content
327When Teams Haven't Migrated Yet
328Should You Write New Class Components?

← React

Lesson 299 of 2,396·9. Class Components (Legacy Overview)Pro lesson

componentWillUnmount: Cleanup Before Removal

Canceling timers, clearing subscriptions, and cleaning up resources before the component disappears.

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