有时候需要让 a 标签像 button 一样，被点击的时候触发事件而不跳转页面。
<html>
<body>
<a id="a1" href="#none" onclick="a_click(this.id)">Click a1</a>
<a id="a2" href="javascript:void(0);" onclick="a_click(this.id)">Click a2</a>
<a id="a3" href="any.html" onclick="a_click(this.id);return false;">Click a3</a>
</body>
<script type="text/javascript">
function a_click (aid) {
alert(aid + " was clicked.");
}
</script>
</html>