怎么样用js得到同一类型的控件

<input   type= "file "   size= "30 "   name= "sdf "> 
<input   type= "file "   size= "30 "   name= "intrfeop1 "> 
<input   type= "file "   size= "30 "   name= "intfasrop "> 
<input   type= "file "   size= "30 "   name= "basd "> 

var   a=document.getElementsByTagName( "input "); 
for(var   i=0;i <a.length;i++){ 
      if(a[i].type== "file "){ 

        ... 
      } 
}