<!DOCTYPE html>
<html>
<head>
<script>
function checkField(val)
{
alert("输入值已改变。新值为: " + val);
}
</script>
</head>
<body>
<p>修改输入域的文本，点击输入域外区域触发 onchange。</p>
输入文本: <input type="text" name="txt" value="Hello" onchange="checkField(this.value)">
</body>
</html>