74 lines
2.2 KiB
HTML
74 lines
2.2 KiB
HTML
<!--
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* @Author: chenxuan
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* @Date: 2022-01-13 23:49:27
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* @LastEditTime: 2022-01-14 00:40:51
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* @LastEditors: chenxuan
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-->
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<!DOCTYPE html>
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<html lang="en">
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<head>
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<meta charset="UTF-8">
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<meta http-equiv="X-UA-Compatible" content="IE=edge">
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<meta name="viewport" content="width=device-width, initial-scale=1.0">
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<title>Document</title>
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<title>getSnapshotBeforeUpdate</title>
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<script src="../package/new/react.development.js"></script>
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<script src="../package/new/react-dom.development.js"></script>
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<script src="../package/new/babel.min.js"></script>
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<style>
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.list{
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width: 150px;
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height: 150px;
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border: 1px solid red;
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overflow-y: auto;
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}
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.list li{
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width: 100%;
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list-style: none;
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height: 30px;
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line-height: 30px;
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}
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</style>
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</head>
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<body>
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<div id="app"></div>
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<script type="text/babel">
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class Count extends React.Component{
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state={news:["新闻"]}
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componentDidMount(){
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setInterval(()=>{
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const {news}=this.state;
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const news_="新闻"+(news.length+1);
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news.unshift(news_);
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this.setState({news:news})
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},1000)
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}
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getSnapshotBeforeUpdate(){
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return this.refs.list.scrollHeight;
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}
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componentDidUpdate(preProps,preState,height){
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this.refs.list.scrollTop+=this.refs.list.scrollHeight-height
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}
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render(){
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// console.log(this.state.news)
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return (
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<div className="list" ref="list">
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{
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this.state.news.map((item,index)=>{
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return (
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<li key={index}>{item}</li>
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)
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})
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}
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</div>
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)
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}
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}
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ReactDOM.render(
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<Count count={1999} />,document.getElementById('app')
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)
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</script>
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</body>
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</html> |