input 只能输入数字，限定输入

1 onkeyup事件

<html>

<head>
    <script src="https://unpkg.com/react@16/umd/react.development.js" crossorigin></script>
    <script src="https://unpkg.com/react-dom@16/umd/react-dom.development.js" crossorigin></script>
    <script src="https://unpkg.com/babel-standalone@6/babel.min.js"></script>
</head>

<body>
    <div id="root"></div>
</body>
<script type="text/babel">
    const e = React.createElement;
    const custom = () => {
        return <input placeholder="请输入"
            onKeyUp={e => e.target.value = e.target.value.replace(/[^\d]/g, '')} />
    }
    const domContainer = document.querySelector('#root');
    ReactDOM.render(e(custom), domContainer);
</script>

</html>

2 onchange配合value

onkeyup事件本质上就是在键盘松开的时候改变input内的值，那直接用onchange和value不就可以了。

<html>

<head>
    <script src="https://unpkg.com/react@16/umd/react.development.js" crossorigin></script>
    <script src="https://unpkg.com/react-dom@16/umd/react-dom.development.js" crossorigin></script>
    <script src="https://unpkg.com/babel-standalone@6/babel.min.js"></script>
</head>

<body>
    <div id="root"></div>
</body>
<script type="text/babel">
    const e = React.createElement;
    const custom = () => {
        const [number, setNumber] = React.useState()
        return <input placeholder="请输入" value={number}
            onChange={e => setNumber(e.target.value.replace(/[^\d]/g, ''))} />
    }
    const domContainer = document.querySelector('#root');
    ReactDOM.render(e(custom), domContainer);
</script>

</html>

动图上可能看不出来，其实我在输入’2’之后疯狂摁字母键
在这里插入图片描述

3 限定输入规则（正则表达）

只能输入数字string.replace(/[\D]/g, ''))
只能输入数字、英文string.replace(/[^A-Za-z0-9]/g, ''))
只能输入数字、英文、下斜杠string.replace(/[\W]/g, ''))
只能输入数字、小数点(不是小数，可以有多个小数点)string.replace(/[^0-9.]/g, ''))

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