JavaScript 实现按钮点击事件监听与判断

<HTML> 
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> 
<HEAD> 
<TITLE></TITLE> 
<script> 
document.onclick=function(e){ 
var evt=e||window.event; 
var tar=evt.target||evt.srcElement; 
if( (tar.tagName.toLowerCase()=="input"&&tar.type=="button") || tar.tagName.toLowerCase()=="button"){ 
alert("你点击的是一个按钮") 
} 
} 
</script> 
</HEAD> 
<BODY> 
<input id="button1" type="button" value="1111"/> 
<input id="button2" type="button" value="2222"/> 
<input id="button3" type="button" value="3333"/> 
<input id="button4" type="button" value="4444"/> 
</BODY> 
</HTML> 
google 浏览器版：
<HTML> 
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> 
<HEAD> 
<TITLE></TITLE> 
<script> 
document.onclick=function()
{ var obj = event.srcElement; 
if(obj.type == "button"){ 
alert(obj.id); } 
} 
</script> 
</HEAD> 
<BODY> 
<input id="button1" type="button" value="1111"/> 
<input id="button2" type="button" value="2222"/> 
<input id="button3" type="button" value="3333"/> 
<input id="button4" type="button" value="4444"/> 
</BODY> 
</HTML>