CheckLayerClass.js

var onRun = function(context) {
	var doc = context.document;
	var selection = context.selection;

	if(selection.count() == 0){
		doc.showMessage("Please select something.");
	}else{
		for(var i = 0; i < selection.count(); i++){
			var layer = selection[i];
			var layerClass = layer.class();
			
			if(layerClass == "MSShapeGroup"){
			  //do something
			} else if (layerClass == "MSBitmapLayer"){
			  //do something
			} else if (layerClass == "MSTextLayer"){
			  //do something
			} else if (layerClass == "MSSymbolInstance"){
			  //do something
			} else if (layerClass == "MSSymbolMaster"){
			  //do something
			} else if (layerClass == "MSArtboardGroup"){
			  //do something
			} else if (layerClass == "MSLayerGroup"){
			  //do something
			}
		}
	}
};