Arik Chakma
1 year ago
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3edd5f7cc1
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772281a8de
6 changed files with 178 additions and 102 deletions
@ -1,30 +1,32 @@ |
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In React functional components, lifecycle-like behaviors are achieved using hooks: |
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1. **Mounting and Cleanup:** |
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Utilizing the useEffect hook with an empty dependency array ([]) ensures the hook runs after the component mounts to the DOM. |
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## Mounting and Unmounting |
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```js |
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useEffect(() => { |
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Utilizing the useEffect hook with an empty dependency array ([]) ensures the hook runs after the component mounts to the DOM. |
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```js |
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useEffect(() => { |
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// do something after component mounts |
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return () => { |
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// do something before component unmounts |
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}; |
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}, []); |
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``` |
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}, []); |
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``` |
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The cleanup function returned within the useEffect callback offers a mechanism for handling tasks when the component is about to **unmount**. |
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The cleanup function returned within the useEffect callback offers a mechanism for handling tasks when the component is about to **unmount**. |
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## Updates |
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2. **Updating:** |
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The useEffect hook, when invoked without a dependency array or with specific dependencies, executes after every render or when specified prop/state changes are detected. |
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The useEffect hook, when invoked without a dependency array or with specific dependencies, executes after every render or when specified prop/state changes are detected. |
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```js |
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useEffect(() => { |
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```js |
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useEffect(() => { |
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// do something after every render |
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}); |
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``` |
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}); |
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``` |
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```js |
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useEffect(() => { |
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```js |
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useEffect(() => { |
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// do something after specific prop/state changes |
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}, [state1, state2]); |
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``` |
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}, [state1, state2]); |
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``` |
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@ -1,11 +0,0 @@ |
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Inline conditionals in React are expressions that can be used to conditionally render elements. They are useful when you want to render different elements based on a condition. They can be used in JSX by wrapping them in curly braces. Some examples of inline conditionals include the `ternary operator`, logical `&&` operator, and the logical `||` operator. |
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```js |
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<div>{condition ? <span>True</span> : <span>False</span>}</div> |
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``` |
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```js |
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<div>{condition && <span>True</span>}</div> |
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``` |
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> Note that you can also use the `if` statement, but it cannot be used inside JSX. It can only be used inside a function body. |
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@ -1,7 +1,39 @@ |
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You can use React's `React.lazy()` function in conjunction with dynamic `import()` to lazily load a component. This is often combined with `Suspense` to display fallback content while the component is being loaded. |
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You can use React's `lazy()` function in conjunction with dynamic `import()` to lazily load a component. This is often combined with `Suspense` to display fallback content while the component is being loaded. |
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```js |
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const MyComponent = React.lazy(() => import('./MyComponent')); |
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// The component has to be exported as a default export |
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export default function RoadmapRender() { |
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return <h1>This is a lazily-loaded component!</h1>; |
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} |
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``` |
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> Using this pattern requires that the component being lazy loaded is exported as a default export. |
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```js |
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import { lazy, Suspense } from 'react'; |
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const LazyRoadmapRender = lazy(() => delay(import('./RoadmapRender'))); |
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export function App() { |
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const [showRoadmapRender, setShowRoadmapRender] = useState(false); |
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return ( |
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<> |
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<button onClick={() => setShowRoadmapRender(true)}> |
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Show RoadmapRender |
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</button> |
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{showRoadmapRender && ( |
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<Suspense fallback={<div>Loading...</div>}> |
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<LazyRoadmapRender /> |
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</Suspense> |
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)} |
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</> |
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); |
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} |
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// Helper function to simulate a 2 seconds delay |
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function delay(promise) { |
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return new Promise((resolve) => setTimeout(resolve, 2000)).then( |
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() => promise |
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); |
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} |
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``` |
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The `RoadmapRender` component is lazily loaded and rendered inside the `Suspense` component. While the component is being loaded, the `Suspense` component will display the fallback content. |
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Suspense is a component in React that lets you specify the fallback content to display while waiting for a component to load. It is used in conjunction with `lazy()` to lazily load components. |
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```js |
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import { lazy, Suspense } from 'react'; |
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const LazyRoadmapRender = lazy(() => import('./RoadmapRender')); |
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export function App() { |
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const [show, setShow] = useState(false); |
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return ( |
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<> |
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<button onClick={() => setShow(true)}>Show</button> |
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{show && ( |
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<Suspense fallback={<div>Loading...</div>}> |
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<LazyRoadmapRender /> |
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</Suspense> |
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)} |
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</> |
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); |
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} |
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``` |
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Until the `RoadmapRender` component is loaded, the `Suspense` component will display the `Loading...` fallback content. |
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`useTransition` hook allows you to mark certain updates as **transitions** so they can be deprioritized, allowing other, more urgent updates to be processed first. This ensures that the UI remains responsive during updates that might take some time. |
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```js |
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import { useTransition, useState } from 'react'; |
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import { Posts } from './Posts'; |
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import { Home } from './Home'; |
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import { Contact } from './Contact'; |
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export function App() { |
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const [isPending, startTransition] = useTransition(); |
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const [page, setPage] = useState('home'); |
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function changePage(newPage: string) { |
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startTransition(() => { |
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setPage(newPage); |
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}); |
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} |
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return ( |
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<> |
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<button onClick={() => changePage('home')}>Home</button> |
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<button onClick={() => changePage('posts')}>Posts</button> |
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<button onClick={() => changePage('contact')}>Contact</button> |
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<hr /> |
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{isPending && <div>Loading...</div>} |
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{page === 'home' && <Home />} |
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{page === 'posts' && <Posts />} |
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{page === 'contact' && <Contact />} |
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</> |
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); |
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} |
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``` |
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```js |
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export function Home() { |
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return <div>Home</div>; |
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} |
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``` |
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```js |
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export function Contact() { |
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return <div>Contact</div>; |
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} |
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``` |
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Posts component is artificially delayed by 500ms to emulate extremely slow code. |
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```js |
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export function Posts() { |
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const items = []; |
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for (let i = 0; i < 500; i++) { |
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items.push(<SlowPost key={i} />); |
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} |
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return <ul>{items}</ul>; |
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} |
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function SlowPost() { |
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const startTime = performance.now(); |
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while (performance.now() - startTime < 1) { |
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// Do nothing for 1 ms per item to emulate extremely slow code |
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} |
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return <li>Post</li>; |
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} |
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``` |
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Now when you click on the `Posts` button, you'll notice that the UI remains responsive and you can still switch to other pages while the posts are loading. Try removing the `startTransition` wrapper around `setPage` in `changePage` to see the difference. |
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