Re: onAfterRendering vs. JSONModel.loadData()

maybe you want to try

heatmap.onAfterRendering = function() {
     if (sap.viz.ui5.Heatmap.prototype.onAfterRendering) {

         sap.viz.ui5.Heatmap.prototype.onAfterRendering.apply(this);

     }

     var model = this.getModel();

     // check if model has data, if yes, do something

}

-D