function bind(el,name,fn){ //綁定事件
return el.addEventListener?el.addEventListener(name,fn,false):el.attachEvent('on'+name,fn);
}

bind(document.getElementById('wrap'),'click',a);
bind(document.getElementById('wrap'),'click',b);

if (elem.addEventListener)
　　　　elem.addEventListener(type, handle, false);
　　else if (elem.attachEvent)
　　　　elem.attachEvent("on" + type, handle);

<script type="text/javascript">
var bind = function(e,t,fn){
if(e.addEventListener){
e.addEventListener(t, fn, false);
}else if(e.attachEvent){
e.attachEvent('on'+ t, fn);
}
}
</script>
<a href="#" id="test1">test</a>
<script type="text/javascript">
var e = document.getElementById('test1');
bind(e,'click',function(){alert(1)});
bind(e,'click',function(){alert(2)});
bind(e,'click',function(){alert(3)});
bind(e,'click',function(){alert(4)});
bind(e,'click',function(){alert(5)});
</script>