javascript 提取<div>的问题！！！

Question

<div id="pub_12">xxxxxxxxxxxxx </div>
<div id="pub_34">xxxxxxxxxxxxx </div>
<div id="pub_56">xxxxxxxxxxxxx </div>
<div id="pub_33">xxxxxxxxxxxxx </div>
<div id="pub_87">xxxxxxxxxxxxx </div>
<div id="pub_44">xxxxxxxxxxxxx </div><script type="text/javascript">
var b=document.getElementsByTagName("div")alert(b.length)
for(var i=0;i<b.length;i++){
//alert(b[i].id)
//alert(b[i].id.length)
    if(b[i].id.length>3){
   if(b[i].id.substr(0,3)=="pub"){
      alert(b[i].id)
   }
}
}</script> 

Answer 1

<div id="erter_pub_12">xxxxxxxxxxxxx </div> 
<div id="11111111pub_34">xxxxxxxxxxxxx </div> 
<div id="fpub_56">xxxxxxxxxxxxx </div> 
<div id="pub_33gg">xxxxxxxxxxxxx </div> 
<div id="dddpub_87">xxxxxxxxxxxxx </div> 
<div id="6666pub_44">xxxxxxxxxxxxx </div>
 如果是提取包涵pub的是不是要用到正则？还是indexOF?