效果图如下：
代码如下：
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Document</title>
</head>
<body>
<div id="box"></div>
<script crossorigin src="https://unpkg.com/react@16/umd/react.development.js"></script>
<script crossorigin src="https://unpkg.com/react-dom@16/umd/react-dom.development.js"></script>
<script src="https://cdn.bootcss.com/babel-standalone/7.0.0-beta.3/babel.js"></script>
<script type="text/babel">
const {useRef} = React
function Compont() {
const username = useRef('初始值可写可不写')
const password = useRef()
const handleClick = () => {
console.log('用户名：' + username.current.value)
console.log('密码：' + password.current.value)
}
return(
<div>
用户名：<input type="text" ref={username} /> <br/>
密码：<input type="password" ref={password} /> <br/>
<button onClick={handleClick}>点击登入</button>
</div>
)
}
ReactDOM.render( <Compont/>, document.getElementById('box'))
</script>
</body>
</html>