JS 一个函数处理多个事件

<script type="text/javascript">
window.onload = function() {
//this指向注册这个事件元素
/**
document.getElementById("testBtn").onclick = function(event) {
alert(event);
alert(event.target);
alert(this);
alert(event.currentTarget);
alert(this === event.currentTarget);
}
*/
var btnNode = document.getElementsByTagName("input").item(0);
var handler = function(event) {
switch (event.type) {
case "click":
alert("clicked");
break;
case "mouseover":
event.currentTarget.style.backgroundColor = "red";
break;
case "mouseout":
event.currentTarget.style.backgroundColor = "";
break;
}
};
btnNode.onclick = handler;
btnNode.onmouseover = handler;
btnNode.onmouseout = handler;
};
</script>