topic Re: map vs app.map in ArcGIS JavaScript Maps SDK Questions

map vs app.map

p_thibault — Mon, 20 Aug 2012 13:12:52 GMT

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.

Re: map vs app.map

ReneRubalcava — Mon, 20 Aug 2012 13:45:29 GMT

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.

Re: map vs app.map

derekswingley1 — Mon, 20 Aug 2012 14:55:30 GMT

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.

You got it. Nothing more to it... trying to avoid polluting the global namespace. To answer the quasi-question, I didn't run into any conflicts with existing object/libraries while writing that sample.