​x
 
<!DOCTYPE html>
<html>
<head>
<script>
function displayResult()
{
    var x;
    if(window.event) // IE8 及更早IE版本
    {
        x=event.keyCode;
    }
    else if(event.which) // IE9/Firefox/Chrome/Opera/Safari
    {
        x=event.which;
    }
    var keychar=String.fromCharCode(x);
    alert("按键 " + keychar + " 被按下");
}
</script>
</head>
<body>
​
<p>当用户在输入域按下按键时触发函数。 该功能提醒按下的键。</p>
​
<input type="text" onkeydown="displayResult()">
​
</body>
</html>