下面是一个简单的alert(）方法，通过HTML+CSS 方式，把提示信息以HTML层的形式显示在页面中
<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title></title>
<style type="text/css">
#alert_box { position: absolute; left: 50%; top: 50%; width: 400px; height: 200px; display:none;}
#alert_box dl { position: absolute; left: -200px; top: -100px; width: 400px; height: 200px; border: solid 1px #999; border-radius: 8px; overflow: hidden; }
#alert_box dt { background-color: #ccc; height: 30px; text-align: center; line-height: 30px; font-weight: bold; font-size: 15px; }
#alert_box dd { padding: 6px; margin: 0; font-size: 12px; }
</style>
</head>
<body>
<script>
window.alert = function(title, info){
var box = document.getElementById("alert_box");
var html = '<dl><dt>' + title + '</dt><dd>' + info + '</dd><\/dl>';
if( box ){
box.innerHTML = html;
box.style.display = "block";
}
else {
var div = document.createElement("div");
div.id = "alert_box";
div.style.display = "block";
document.body.appendChild(div);
div.innerHTML = html;
}
}
alert("重写alert()方法", "这仅是一个设计思路，还可以进一步设计");
</script>
</body>
</html>