Function interval

test/angular/1.6/angular.js:13593–13634

* @ngdoc service * @name $interval * * @description * AngularJS's wrapper for `window.setInterval`. The `fn` function is executed every `delay` * milliseconds. * * The return value of registering an interval function is a promise. This promise will be * notifi

(fn, delay, count, invokeApply)

     * </example>
     */
    function interval(fn, delay, count, invokeApply) {
      var hasParams = arguments.length > 4,
          args = hasParams ? sliceArgs(arguments, 4) : [],
          setInterval = $window.setInterval,
          clearInterval = $window.clearInterval,
          iteration = 0,
          skipApply = (isDefined(invokeApply) && !invokeApply),
          deferred = (skipApply ? $$q : $q).defer(),
          promise = deferred.promise;

      count = isDefined(count) ? count : 0;

      promise.$$intervalId = setInterval(function tick() {
        if (skipApply) {
          $browser.defer(callback);
        } else {
          $rootScope.$evalAsync(callback);
        }
        deferred.notify(iteration++);

        if (count > 0 && iteration >= count) {
          deferred.resolve(iteration);
          clearInterval(promise.$$intervalId);
          delete intervals[promise.$$intervalId];
        }

        if (!skipApply) $rootScope.$apply();

      }, delay);

      intervals[promise.$$intervalId] = deferred;

      return promise;

      function callback() {
        if (!hasParams) {
          fn(iteration);
        } else {
          fn.apply(null, args);
        }
      }
    }


    /**