欢迎吐槽讨论
前言
笔者在React经常使用setState，在学习过程中作笔记以作总结，欢迎讨论。
关于setState的核心观点
1 . 执行setState不都是异步的。
2 . setState能够缓存多次结果，对最晚的setState进行更新 ( batchedUpdate 批次式更新 )
代码部分
// typescript
let stateList = [];
let LOCK = false;
const ele = document.getElementById('test');
const view = document.getElementById('v');
const setState = (arg)=>{
if(!LOCK){
render(arg)
}else{
stateList.push(arg);
}
}
const render = (arg)=>{
alert('我只执行了一次render');
view.innerHTML = arg
}
// 启动
ele.onclick = function() {
const myT = new Transaction();
myT.perform(()=>{
console.log('i am cb');
setState('ONE');
setState('TWO');
setState('THREE');
setState('FOUR');
});
} class Transaction {
constructor() { }
_init() {
// 上锁
LOCK = true;
console.log('i am init');
}
_close() {
LOCK = false;
console.log('i am close');
// batch update
setState(stateList.pop());
// 解锁、清空stateList
stateList = []; }
async perform(cb){
await this._init();
cb();
await this._close();
}
}
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<title>Document</title>
</head>
<body>
<h2>每次执行setState不应该都进行render，而是应该render最后一次setState，观察console更佳</h2>
<h3 id="test">点我</h3>
<h3 id="v"></h3>
<pre>
ele.onclick = function() {
const myT = new Transaction();
myT.perform(()=>{
console.log('i am cb');
setState('ONE');
setState('TWO');
setState('THREE');
setState('FOUR');
});
}
</pre>
<script src="batchUpdate.js"></script>
</body>
</html>