触发别的按钮的onclick事件

<html>
<head>
<title>dddd</title><script type="text/javascript">

function trigbutton(){

       var comment = document.getElementById('button2');

           if (document.all) {
           // For IE
           comment.click();
           }
           else if (document.createEvent) {
           //FOR DOM2
           var ev = document.createEvent('HTMLEvents');
           ev.initEvent('click', false, true);
           comment.dispatchEvent(ev);
           }

       }

       function trigselect(){

       var comment = document.getElementById('button3');

       comment.click();
       }

</script>
</head>

<body>
<select size="1" name="D1" id="select1">
<option>1</option>
<option>2</option>
<option>3</option>
<option>4</option>
</select>
<input type="button" value="button1" onclick="alert('button1');trigbutton();"/>
<input type="button" value="button2"id="button2" onclick="alert('button2');trigselect();"/>
<input type="button" value="button3"id="button3" onclick="alert('button3');"/>
</body>
</html>