React Hooks append state
setTheArray(currentArray => [...currentArray, newElement])React Hooks append state
setTheArray(currentArray => [...currentArray, newElement])usestate hook
import React, { useState } from 'react';
function Example() {
// Declare a new state variable, which we'll call "count"
const [count, setCount] = useState(0);
return (
<div>
<p>You clicked {count} times</p>
<button onClick={() => setCount(count + 1)}>
Click me
</button>
</div>
);
}react useEffect
import React, { useEffect, useState } from 'react';
import ReactDOM from 'react-dom';
function LifecycleDemo() {
// It takes a function
useEffect(() => {
// This gets called after every render, by default
// (the first one, and every one after that)
console.log('render!');
// If you want to implement componentWillUnmount,
// return a function from here, and React will call
// it prior to unmounting.
return () => console.log('unmounting...');
}, [ // dependencies to watch = leave blank to run once or you will get a stack overflow ]);
return "I'm a lifecycle demo";
}
function App() {
// Set up a piece of state, just so that we have
// a way to trigger a re-render.
const [random, setRandom] = useState(Math.random());
// Set up another piece of state to keep track of
// whether the LifecycleDemo is shown or hidden
const [mounted, setMounted] = useState(true);
// This function will change the random number,
// and trigger a re-render (in the console,
// you'll see a "render!" from LifecycleDemo)
const reRender = () => setRandom(Math.random());
// This function will unmount and re-mount the
// LifecycleDemo, so you can see its cleanup function
// being called.
const toggle = () => setMounted(!mounted);
return (
<>
<button onClick={reRender}>Re-render</button>
<button onClick={toggle}>Show/Hide LifecycleDemo</button>
{mounted && <LifecycleDemo/>}
</>
);
}
ReactDOM.render(<App/>, document.querySelector('#root'));Copyright © 2021 Codeinu
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