<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>W3Cschool在线教程(w3cschool.cn)</title>
<script>
function myFunction(){
alert("你在输入栏内按下一个键");
}
</script>
</head>
<body>
<p>当你在输入框内按下一个按键是函数被触发</p>
<input type="text" onkeydown="myFunction()">
</body>
</html>