What is Facebook's function __d

Question

I'm working on a project that (hopefully) involves taking advantage of some of the javascript that's already built into Facebook. But right away I've got a roadblock in that I can't figure out what __d is.

If you look at the source javascript files, pretty much every command begins with __d

For example:

__d("legacy:live-timer",["LiveTimer"],function(a,b,c,d){a.LiveTimer=b('LiveTimer');},3);

But I can't find anywhere in any of the javascript files what __d actually does. Shouldn't it have to be defined somewhere for all these other functions to take advantage of it?

UPDATE:

So let's say there's a site with some javascript like this...

function alertSomething(var) {
    if (var) alert("Here it is: "+var);
}

if (some condition) alertSomething("something");

Now let's say I had a Chrome Extension and I was able to inject my own Javascript into the page. Couldn't \my Chrome Extension Javascript have something like this...

if (some other condition) alertSomething("something else");

Thus I would be taking advantage of some code that exists in the javascript already on the page?

Answer 1

As, I have inspected Facebook JavaScript SDK. I believe that it uses Dependency Injection Mechanism. Here are two URLs.

Production: http://connect.facebook.net/en_US/all.js (obfuscated)

Development: http://connect.facebook.net/en_US/all/debug.js (deobfuscated)

If you check debug.js, you can see require, __d, __t and many more. __d is more like define function from RequireJS (http://requirejs.org/docs/api.html#define)

__d = function(/*string*/ id, /*array<string>*/ deps, factory,
      /*number?*/ _special) {/*TC*/__t([id,'string','id'],[deps,'array<string>','deps'],[_special,'number?','_special']);/*/TC*/

Answer 2

I found the definition of __d on line 20 of 1LWPxIBQ4v0.js. No idea if the file is named the same for everyone. Search for "a.__d=function(s,t,u,v)" (a is the global object, i.e. window, effectively making __d a global function). Good luck with that de-minification though...