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React-Diffing算法和key的作用

news 2025/7/19 8:06:58

1.验证Diffing算法

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <div id="test"></div>
    <script src="../js/17.0.1/react.development.js "></script>
    <script src="../js/17.0.1/react-dom.development.js"></script>
    <script src="../js/17.0.1/babel.min.js"></script>
    <!-- 对标签属性进行限制 -->
    <script src="../js/17.0.1/prop-types.js"></script>
    <script type="text/babel">
        class Time extends React.Component {
            state = { date: new Date() }
            componentDidMount() {
                setInterval(() => {
                    this.setState({ date: new Date() })
                }, 1000)
            }
            render() {
                return (<div>现在时间是{this.state.date.toTimeString()}
                    <input type="text" /></div>)
            }
        }
        ReactDOM.render(<Time />, document.getElementById('test'))
    </script>
</body>

</html>

在这里插入图片描述
这段代码是一个使用 React 编写的时钟组件，它会每秒更新一次当前时间并显示在页面上,输入框的数据始终没变,是因为Diffing算法

diffing 算法通过比较虚拟 DOM 树的差异，只更新实际 DOM 中发生变化的部分

2.key的作用

在这里插入图片描述

若使用index作为key值:请看代码

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <div id="test"></div>
    <script src="../js/17.0.1/react.development.js "></script>
    <script src="../js/17.0.1/react-dom.development.js"></script>
    <script src="../js/17.0.1/babel.min.js"></script>
    <!-- 对标签属性进行限制 -->
    <script src="../js/17.0.1/prop-types.js"></script>
    <script type="text/babel">
        class Person extends React.Component {
            state = {
                persons: [
                    { id: 1, name: "小李", age: 18 },
                    { id: 2, name: "小张", age: 19 }
                ]
            }
            add = () => {
                const { persons } = this.state
                const p = { id: persons.length, name: '小王', age: 20 }
                this.setState({ persons: [p, ...persons] })
            }

            render() {
                return (<div>
                    {this.state.persons.map((item, index) => <li key={index}>{item.name}, {item.age}</li>)}
                    <button onClick={this.add}>添加小王</button>
                </div>)
            }
        }
        ReactDOM.render(<Person />, document.getElementById('test'))
    </script>
</body>

</html>