Effect Hooks
Effects let a component connect to and synchronize with external systems. This includes dealing with network, browser DOM, animations, widgets written using a different UI library, and other non-React code.
useEffect connects a component to an external system.
function ChatRoom ( { roomId } ) {
useEffect ( ( ) => {
const connection = createConnection ( roomId ) ;
connection . connect ( ) ;
return ( ) => connection . disconnect ( ) ;
} , [ roomId ] ) ;
// ...
Effects are an “escape hatch” from the React paradigm. Don’t use Effects to orchestrate the data flow of your application. If you’re not interacting with an external system, you might not need an Effect.
There are two rarely used variations of useEffect with differences in timing:
useLayoutEffect fires before the browser repaints the screen. You can measure layout here.useInsertionEffect fires before React makes changes to the DOM. Libraries can insert dynamic CSS here.
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Built-in React Hooks – Reactt most often it’s used to hold a DOM node. useImperativeHandle lets you customize the ref exposed by your component. This is rarely used. function Form() { const inputRef = useRef(null); // ... <span>Effect Hooks Effects let a component connect to and synchronize with external systems. This includes dealing with network, browser DOM, animations, widgets written using a different UI library, and other non-React code. useEffect connects a component to an external system. function ChatRoom({ roomId }) { useEffect(() => { const connection = createConnection(roomId); connection.connect(); return () => connection.disconnect(); }, [roomId]); // ... Effects are an “escape hatch” from the React paradigm. Don’t use Effects to orchestrate the data flow of your application. If you’re not interacting with an external system, you might not need an Effect. There are two rarely used variations of useEffect with differences in timing: useLayoutEffect fires before the browser repaints the screen. You can measure layout here. useInsertionEffect fires before React makes changes to the DOM. Libraries can insert dynamic CSS here. Performance Hooks A common way to optimize re-rendering performance is to skip unnecessary work. For example, you can tell React to reuse a cached calculation or to skip a re-render if Summary
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