docs: function diffData(oldData, newData) {
      var diffResult = [];
  
      newData.diff(oldData)
          .add(function (idx) {
              diffResult.push({cmd: '+', idx: idx});
          })
          .update(function (newIdx, oldIdx) {
              diffResult.push({cmd: '=', idx: oldIdx, idx1: newIdx});
          })
          .remove(function (idx) {
              diffResult.push({cmd: '-', idx: idx});
          })
          .execute();
  
      return diffResult;
  }