code: function (index, item) {
          if (index !== this.length) {
              validateListIndex(this, index);
          }
  
          var len = ++this.length;
  
          while (len-- > index) {
              this[len] = this[len - 1];
          }
  
          this[index] = item;
      }
docs: Inserts an element into the List at the specified index.
  @param {Number} index The zero-based index at which item should be inserted.
  @param {Object} item The object to insert.