Arik Chakma
1 year ago
parent
3edd5f7cc1
commit
772281a8de
6 changed files with 178 additions and 102 deletions
@ -1,30 +1,32 @@ |
||||
In React functional components, lifecycle-like behaviors are achieved using hooks: |
||||
|
||||
1. **Mounting and Cleanup:** |
||||
Utilizing the useEffect hook with an empty dependency array ([]) ensures the hook runs after the component mounts to the DOM. |
||||
|
||||
```js |
||||
useEffect(() => { |
||||
// do something after component mounts |
||||
return () => { |
||||
// do something before component unmounts |
||||
}; |
||||
}, []); |
||||
``` |
||||
|
||||
The cleanup function returned within the useEffect callback offers a mechanism for handling tasks when the component is about to **unmount**. |
||||
|
||||
2. **Updating:** |
||||
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. |
||||
|
||||
```js |
||||
useEffect(() => { |
||||
// do something after every render |
||||
}); |
||||
``` |
||||
|
||||
```js |
||||
useEffect(() => { |
||||
// do something after specific prop/state changes |
||||
}, [state1, state2]); |
||||
``` |
||||
## Mounting and Unmounting |
||||
|
||||
Utilizing the useEffect hook with an empty dependency array ([]) ensures the hook runs after the component mounts to the DOM. |
||||
|
||||
```js |
||||
useEffect(() => { |
||||
// do something after component mounts |
||||
return () => { |
||||
// do something before component unmounts |
||||
}; |
||||
}, []); |
||||
``` |
||||
|
||||
The cleanup function returned within the useEffect callback offers a mechanism for handling tasks when the component is about to **unmount**. |
||||
|
||||
## Updates |
||||
|
||||
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. |
||||
|
||||
```js |
||||
useEffect(() => { |
||||
// do something after every render |
||||
}); |
||||
``` |
||||
|
||||
```js |
||||
useEffect(() => { |
||||
// do something after specific prop/state changes |
||||
}, [state1, state2]); |
||||
``` |
||||
|
||||
@ -1,11 +0,0 @@ |
||||
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. |
||||
|
||||
```js |
||||
<div>{condition ? <span>True</span> : <span>False</span>}</div> |
||||
``` |
||||
|
||||
```js |
||||
<div>{condition && <span>True</span>}</div> |
||||
``` |
||||
|
||||
> 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. |
||||
@ -1,7 +1,39 @@ |
||||
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. |
||||
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. |
||||
|
||||
```js |
||||
const MyComponent = React.lazy(() => import('./MyComponent')); |
||||
// The component has to be exported as a default export |
||||
export default function RoadmapRender() { |
||||
return <h1>This is a lazily-loaded component!</h1>; |
||||
} |
||||
``` |
||||
|
||||
> Using this pattern requires that the component being lazy loaded is exported as a default export. |
||||
```js |
||||
import { lazy, Suspense } from 'react'; |
||||
|
||||
const LazyRoadmapRender = lazy(() => delay(import('./RoadmapRender'))); |
||||
|
||||
export function App() { |
||||
const [showRoadmapRender, setShowRoadmapRender] = useState(false); |
||||
return ( |
||||
<> |
||||
<button onClick={() => setShowRoadmapRender(true)}> |
||||
Show RoadmapRender |
||||
</button> |
||||
{showRoadmapRender && ( |
||||
<Suspense fallback={<div>Loading...</div>}> |
||||
<LazyRoadmapRender /> |
||||
</Suspense> |
||||
)} |
||||
</> |
||||
); |
||||
} |
||||
|
||||
// Helper function to simulate a 2 seconds delay |
||||
function delay(promise) { |
||||
return new Promise((resolve) => setTimeout(resolve, 2000)).then( |
||||
() => promise |
||||
); |
||||
} |
||||
``` |
||||
|
||||
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. |
||||
|
||||
@ -0,0 +1,23 @@ |
||||
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. |
||||
|
||||
```js |
||||
import { lazy, Suspense } from 'react'; |
||||
|
||||
const LazyRoadmapRender = lazy(() => import('./RoadmapRender')); |
||||
|
||||
export function App() { |
||||
const [show, setShow] = useState(false); |
||||
return ( |
||||
<> |
||||
<button onClick={() => setShow(true)}>Show</button> |
||||
{show && ( |
||||
<Suspense fallback={<div>Loading...</div>}> |
||||
<LazyRoadmapRender /> |
||||
</Suspense> |
||||
)} |
||||
</> |
||||
); |
||||
} |
||||
``` |
||||
|
||||
Until the `RoadmapRender` component is loaded, the `Suspense` component will display the `Loading...` fallback content. |
||||
@ -0,0 +1,67 @@ |
||||
`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. |
||||
|
||||
```js |
||||
import { useTransition, useState } from 'react'; |
||||
import { Posts } from './Posts'; |
||||
import { Home } from './Home'; |
||||
import { Contact } from './Contact'; |
||||
|
||||
export function App() { |
||||
const [isPending, startTransition] = useTransition(); |
||||
const [page, setPage] = useState('home'); |
||||
|
||||
function changePage(newPage: string) { |
||||
startTransition(() => { |
||||
setPage(newPage); |
||||
}); |
||||
} |
||||
|
||||
return ( |
||||
<> |
||||
<button onClick={() => changePage('home')}>Home</button> |
||||
<button onClick={() => changePage('posts')}>Posts</button> |
||||
<button onClick={() => changePage('contact')}>Contact</button> |
||||
<hr /> |
||||
{isPending && <div>Loading...</div>} |
||||
{page === 'home' && <Home />} |
||||
{page === 'posts' && <Posts />} |
||||
{page === 'contact' && <Contact />} |
||||
</> |
||||
); |
||||
} |
||||
``` |
||||
|
||||
```js |
||||
export function Home() { |
||||
return <div>Home</div>; |
||||
} |
||||
``` |
||||
|
||||
```js |
||||
export function Contact() { |
||||
return <div>Contact</div>; |
||||
} |
||||
``` |
||||
|
||||
Posts component is artificially delayed by 500ms to emulate extremely slow code. |
||||
|
||||
```js |
||||
export function Posts() { |
||||
const items = []; |
||||
for (let i = 0; i < 500; i++) { |
||||
items.push(<SlowPost key={i} />); |
||||
} |
||||
return <ul>{items}</ul>; |
||||
} |
||||
|
||||
function SlowPost() { |
||||
const startTime = performance.now(); |
||||
while (performance.now() - startTime < 1) { |
||||
// Do nothing for 1 ms per item to emulate extremely slow code |
||||
} |
||||
|
||||
return <li>Post</li>; |
||||
} |
||||
``` |
||||
|
||||
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. |
||||
Loading…
Reference in new issue