Question

can someone please explain what’s the exports variable for:

copied from backbone.js, I also noticed spine.js uses the same pattern.

https://gist.github.com/1375748

var Backbone;
if (typeof exports !== 'undefined') {
    Backbone = exports;
} else {
    Backbone = root.Backbone = {};
}

Answer 1

That module pattern is part of the CommonJS specification called CommonJS Modules:

In a module, there is a free variable called “exports”, that is an
object that the module may add its API to as it executes.

So basically adding to the exports object defines the API your module exposes.