I recently found that AngularJS has supports for promises. I replaced some of the callback code to use promises and it's a lot more readable.

Callbacks:

    Backend.CallA(param, function() { 
      aDone = true;
      if (aDone && bDone) { doC(); }
    });
    Backend.CallB(param, function() { 
      bDone = true;
      if (aDone && bDone) { doC(); }
    });

Promises:

    var promiseA = Backend.CallA(param);
    var promiseB = Backend.CallB(param);
    $q.all([promiseA, promiseB]).then(doC);