code: function (index, collection) {
          assertType(index, Number);
          assertNotNull(collection);
  
          if (index !== this.length) {
              validateListIndex(this, index);
          }
  
          var arr = buffer(collection),
              count = arr.length,
              len = this.length + count;
  
          this.length = len;
  
          while (len-- > index) {
              this[len] = this[len - count];
          }
  
          while (count-- > 0) {
              this[index + count] = arr[count];
          }
      }
docs: Inserts the elements of a collection into the List at the specified index.
  @param {Number} index The zero-based index at which item should be inserted.
  @param {Iterable} collection The collection whose elements should be inserted into the List.