map vs app.map

p_thibault

In the new print widget the examples show the map being defined as:
var app = {};
app.map = null,
app.map = new esri.Map("map", {
          extent: initialExtent,
          wrapAround180: true
        });

this is compared to just :
map = new esri.Map.........

Can some please explain what is happening with the variable "app"?

Thanks.

RRubalcava

It looks like the sample was written to keep application specific objects in their own namespace.

For example, when you write

var map = new esri.Map("map");

'map' is bound to the Window object of the browser, which is basically the global namespace.
By declaring

var app = {}; // This is an empty object, equivalient to window.app app.map = new esri.Map("map"); // map is now bound to window.app.map

In the print widjet example, all the application specific values are now in window.app (map, printer, symbols, toolbar).
It's a method of organizing the code in the application.

It's interesting that it's done in the Print Widget, I don't think I've seen it in other esri js samples before. It's not a strict rule, more of a best practices kind of thing to keep the global namespace clean. It's not mentioned their coding guidelines. In this case maybe there are othe common libraries that may already have a window.printer object defined and they wanted to avoid overrriding it.