what is this underscore.js “safe reference” code doing?

Question

I\'m learning Backbone, which uses Underscore.

In some examples, I see initialization code to create an empty array of children like this:

// inside          


        

Answer 1

Because this.children needs to be a instance of underscore: a specialized class that wraps an array, not just a regular javascript array literal. The code in the _ function just makes sure it's always one _ instance wrapping one regular array, even if you try to rewrap an underscore instance repeatedly, call _ with or without the new keyword.

//new _ instance wrapping an array. Straightforward.
var _withNew = new _([]);

//automatically calls `new` for you and returns that, resulting in same as above
var _withoutNew = _([]);

//just gives you _withoutNew back since it's already a proper _ instance
var _doubleWrapped = _(_withoutNew);