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 "){         ...       } }