code: function updateSimple(newList, oldList, rawNewValue ){
  
      var nlen = newList.length;
      var olen = oldList.length;
      var mlen = Math.min(nlen, olen);
  
      updateRange(0, mlen, newList, rawNewValue)
      if(nlen < olen){ //need add
        removeRange(nlen, olen-nlen, children);
      }else if(nlen > olen){
        addRange(olen, nlen, newList, rawNewValue);
      }
    }
docs: if the track is constant test.