Fields caption

Hello, I am working with the pivot table and I would like to set the title fields before knowing which fields will be used in the pivot table. In web examples, the title is already defined in dataSourceSettings. But in my case the data source will change and I don't know which fields were chosen.

enginePopulated: function(args) {     var captions = ['A', 'B', 'C', 'D', 'E', 'F', 'G']     var i=0;     var obj = this.engineModule.fieldList;     for (var key in obj) {       if (obj.hasOwnProperty(key)) {         this.engineModule.fieldList[key].caption = captions[i];         i++;       }     }  }