Q:

JS: truly secret vars (for securely submitting a score)

Is it possible to find a randomly generated value declared within an anonymous function (IIFE), and if so how?
(function () {
  // assuming an epic, obscured, random function
  var salt = random()*10000|0;

  // assuming an event manager
  Events.on('custom event', function () {
    // do something amazing with salt here
  });
})()

Assuming: 

the function is loaded via ajax
it executes on load (making it difficult to include a breakpoint)
there's a suitably elegant solution in place to test for injection (is there such a thing?).

A:

A simple breakpoint in your JS exposes the salt value. It is not accessible to code outside the IIFE (Immediately Invoked Function Expression - what you are calling anonymous function), but if you're trying to keep a debugger from seeing it via a breakpoint inside the IIFE, then JS is not going to prevent that in any way.
For example, you can set a breakpoint right where the salt value is coined and see what it is or if that code is dynamically loaded via ajax, you can set a breakpoint on the ajax loading code and then step through the loading of the code until you can then set a breakpoint where the sale value is coined.

