[Deff]

<div id='elem_container'>
   <div id='elem_14'>
      <div class='bla_bla_bla'>1
        <div .... ></div>
      </div>
   </div>
   <div id='elem_674564564'>2
      <div class='bla_bla_bla'>
        <div .... ></div>
      </div>
   </div>
   <div id='elem_086757'>3
      <div class='bla_bla_bla'>
        <div .... ></div>
      </div>
   </div>

</div>

<script type="text/javascript">
var StDoc = document.getElementById('elem_container');//alert(StDoc.innerHTML)
var FndDivs = StDoc.getElementsByTagName('div')
var FindId = 'elem_';
var Length = FndDivs.length;
var MyArray = [];

for(i=0; i<Length; i++){
  if(FndDivs[i].id.indexOf(FindId)) continue;
  MyArray.push(FndDivs[i])
}
MyArray[1].style.background='red'
alert(MyArray[1].style.background)

</script>