Repository: angular/angular.js
File: src/ng/rootScope.js (JavaScript)

Code before:
       * @description
       * Listens on events of a given type. See {@link ng.$rootScope.Scope#$emit $emit} for
       * discussion of event life cycle.
       *
       * The event listener function format is: `function(event, args...)`. The `event` object
       * passed into the listener has the following attributes:
       *
       *   - `targetScope` - `{Scope}`: the scope on which the event was `$emit`-ed or
       *     `$broadcast`-ed.
       *   - `currentScope` - `{Scope}`: the scope that is currently handling the event. Once the
       *     event propagates through the scope hierarchy, this property is set to null.
       *   - `name` - `{string}`: name of the event.
       *   - `stopPropagation` - `{function=}`: calling `stopPropagation` function will cancel
       *     further event propagation (available only for events that were `$emit`-ed).
       *   - `preventDefault` - `{function}`: calling `preventDefault` sets `defaultPrevented` flag
       *     to true.
       *   - `defaultPrevented` - `{boolean}`: true if `preventDefault` was called.
       *
       * @param {string} name Event name to listen on.
       * @param {function(event, ...args)} listener Function to call when the event is emitted.
       * @returns {function()} Returns a deregistration function for this listener.
       */
      $on: function(name, listener) {
        var namedListeners = this.$$listeners[name];
        if (!namedListeners) {
          this.$$listeners[name] = namedListeners = extend([], {$$index: -1});
        }
        namedListeners.push(listener);

        var current = this;
        do {
          if (!current.$$listenerCount[name]) {
            current.$$listenerCount[name] = 0;
          }
          current.$$listenerCount[name]++;
        } while ((current = current.$parent));

        var self = this;
        return function() {
          var index = arrayRemove(namedListeners, listener);
          if (index >= 0) {
            decrementListenerCount(self, 1, name);
            // We are removing a listener while iterating over the list of listeners.
            // Update the current $$index if necessary to ensure no listener is skipped.
            if (index <= namedListeners.$$index) {
              namedListeners.$$index--;
            }
          }
        };
      },


Review comment (suggestion):
I think I'll drop this line and use `undefined` instead of `-1` as the "not looping right now" value

Code after:
       * @description
       * Listens on events of a given type. See {@link ng.$rootScope.Scope#$emit $emit} for
       * discussion of event life cycle.
       *
       * The event listener function format is: `function(event, args...)`. The `event` object
       * passed into the listener has the following attributes:
       *
       *   - `targetScope` - `{Scope}`: the scope on which the event was `$emit`-ed or
       *     `$broadcast`-ed.
       *   - `currentScope` - `{Scope}`: the scope that is currently handling the event. Once the
       *     event propagates through the scope hierarchy, this property is set to null.
       *   - `name` - `{string}`: name of the event.
       *   - `stopPropagation` - `{function=}`: calling `stopPropagation` function will cancel
       *     further event propagation (available only for events that were `$emit`-ed).
       *   - `preventDefault` - `{function}`: calling `preventDefault` sets `defaultPrevented` flag
       *     to true.
       *   - `defaultPrevented` - `{boolean}`: true if `preventDefault` was called.
       *
       * @param {string} name Event name to listen on.
       * @param {function(event, ...args)} listener Function to call when the event is emitted.
       * @returns {function()} Returns a deregistration function for this listener.
       */
      $on: function(name, listener) {
        var namedListeners = this.$$listeners[name];
        if (!namedListeners) {
          this.$$listeners[name] = namedListeners = [];
        }
        namedListeners.push(listener);

        var current = this;
        do {
          if (!current.$$listenerCount[name]) {
            current.$$listenerCount[name] = 0;
          }
          current.$$listenerCount[name]++;
        } while ((current = current.$parent));

        var self = this;
        return function() {
          var index = arrayRemove(namedListeners, listener);
          if (index >= 0) {
            decrementListenerCount(self, 1, name);
            // We are removing a listener while iterating over the list of listeners.
            // Update the current $$index if necessary to ensure no listener is skipped.
            if (index <= namedListeners.$$index) {
              namedListeners.$$index--;
            }
          }
        };
      },