<!DOCTYPE html>
<html>
<head>
<script>
function displayResult()
{
var x;
if(window.event) // IE8 以及更早版本
x=event.keyCode;
}
else if(event.which) // IE9/Firefox/Chrome/Opera/Safari
x=event.which;
keychar=String.fromCharCode(x);
alert("按键 " + keychar + " 被按下");
</script>
</head>
<body>
<p>当用户在输入字段中按下按键时触发函数。此函数提示用户已按按键。</p>
<input type="text" onkeypress="displayResult()">
</body>
</html>