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>
);
}hooks in react
import React, { useState, useEffect } from "react";
export default props => {
console.log("componentWillMount");
console.log("componentWillReceiveProps", props);
const [x, setX] = useState(0);
const [y, setY] = useState(0);
const [moveCount, setMoveCount] = useState(0);
const [cross, setCross] = useState(0);
const mouseMoveHandler = event => {
setX(event.clientX);
setY(event.clientY);
};
useEffect(() => {
console.log("componentDidMount");
document.addEventListener("mousemove", mouseMoveHandler);
return () => {
console.log("componentWillUnmount");
document.removeEventListener("mousemove", mouseMoveHandler);
};
}, []); // empty-array means don't watch for any updates
useEffect(
() => {
// if (componentDidUpdate & (x or y changed))
setMoveCount(moveCount + 1);
},
[x, y]
);
useEffect(() => {
// if componentDidUpdate or componentDidMount
if (x === y) {
setCross(x);
}
});
return (
<div>
<p style={{ color: props.color }}>
Your mouse is at {x}, {y} position.
</p>
<p>Your mouse has moved {moveCount} times</p>
<p>
X and Y positions were last equal at {cross}, {cross}
</p>
</div>
);
};Copyright © 2021 Codeinu
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