code: function updateTrack( newList, oldList, steps,  rawNewValue, oldKeyMap ){
      
      for(var i =0, slen = steps.length; i < slen ;i++){
        var step = steps[i];
        switch( step.mode){
          case 0 : //remove
            removeRange(step.index, step.len, group.children, oldKeyMap);
            break;
          case 1 : //insert
            addRange(step.index, step.index + step.len, newList, rawNewValue, oldKeyMap )
            break;
        }
      }     
      var children = group.children;
      for(var j=1, len = children.length; j < len; j++){
        var child = children[j];
        if( child ){
          child.data[variable] = newList[j-1];
          child.data[indexName] = j-1
        }
      }
  
      
    }
docs: oldKeyMap: 复用原来的节点