var classDef = new ClassBreaksDefinition();
<<< classDef.classificationField = app.currentAttribute; >>>
<<< assign an Array here instead of the line before >>>
//Known values: natural-breaks | equal-interval | quantile | standard-deviation | geometrical-interval
classDef.classificationMethod = "natural-breaks";
classDef.breakCount = 5;
classDef.baseSymbol = app.symbol;