code: function subscribe(bundleIds, callbackFn) {
  	      // listify
  	      bundleIds = bundleIds.push ? bundleIds : [bundleIds];
  	      var depsNotFound = [],
  	          i = bundleIds.length,
  	          numWaiting = i,
  	          fn,
  	          bundleId,
  	          r,
  	          q; // define callback function
  
  	      fn = function fn(bundleId, pathsNotFound) {
  	        if (pathsNotFound.length) depsNotFound.push(bundleId);
  	        numWaiting--;
  	        if (!numWaiting) callbackFn(depsNotFound);
  	      }; // register callback
  
  
  	      while (i--) {
  	        bundleId = bundleIds[i]; // execute callback if in result cache
  
  	        r = bundleResultCache[bundleId];
  
  	        if (r) {
  	          fn(bundleId, r);
  	          continue;
  	        } // add to callback queue
  
  
  	        q = bundleCallbackQueue[bundleId] = bundleCallbackQueue[bundleId] || [];
  	        q.push(fn);
  	      }
  	    }
docs: Subscribe to bundle load event.
  @param {string[]} bundleIds - Bundle ids
  @param {Function} callbackFn - The callback function