How to set the map extent so as to show conccurently all the features included in different map layers

I want to load may diffent layers on my map using the ArcGis JS API. I want to set my map's extent so as to show all the features of all the layers concurrently. In other words I am looking for the extent that contains all my layers graphics and zoom to it.

How can I tell the map to find and zoom to a specific extent that will include all that features? Is there any way other than iterating over all the features, like it is happening in the suggested solution of the this example ?