var App = function(start, cb) {
  var pendingRecursive = 0;
  var eventEmitter = new EventEmitter();
  cb(eventEmitter);

  var Recursive = function(a) {
    // breadth-first search recursion

    // before each recursive call:
    pendingRecursive++;
    Recursive(/*whatever*/);

    // at the end of the function
    if (--activeRecursive == 0){
      eventEmitter.emit('end');
    }
  }

  pendingRecursive = 1;
  Rec