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gaia/apps/settings/js/modules/base/event_emitter.js

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+define(function(require) {
+  'use strict';
+
+  var Module = require('modules/base/module');
+
+  /**
+   * EventEmitter implements basic event emitting logics. It also provides
+   * function that augments the ability to other objects.
+   *
+   * @example
+   *   var eventEmitter = EventEmitter(['event1', 'event2']);
+   *   var eventHandler = function(event) {
+   *     console.log(event.detail);
+   *   };
+   *   var obj = {
+   *     handleEvent: function(event) {
+   *       console.log(event.detail);
+   *     }
+   *   };
+   *
+   *   eventEmitter.addEventListener('event1', eventHandler);
+   *   eventEmitter.addEventListener('event2', obj);
+   *
+   *   eventEmitter._emitEvent('event1', 'value1'); // value1
+   *   eventEmitter._emitEvent('event2', 'value2'); // value2
+   *
+   * Extending from EventEmitter:
+   * @example
+   *   var NewModule = Module.create(function() {
+   *     this.super(EventEmitter).call(this, ['event1', 'event2']);
+   *   }).extend(EventEmitter);
+   *
+   *   var module = NewModule();
+   *
+   * @class EventEmitter
+   * @returns {EventEmitter}
+   */
+  var EventEmitter = Module.create(function EventEmitter(eventNames) {
+    if (eventNames && eventNames.length) {
+      this._eventListeners = eventNames.reduce((result, eventName) => {
+        result[eventName] = [];
+        return result;
+      }, {});
+    } else {
+      this.throw('no valid registered events');
+    }
+  });
+
+  /**
+   * Emit an event of a specific type and a given value.
+   *
+   * @access private
+   * @memberOf EventEmitter.prototype
+   * @param {String} eventName
+   * @param {Object} value
+   */
+  EventEmitter.prototype._emitEvent = function(eventName, value) {
+    var listeners = this._eventListeners[eventName];
+    if (!listeners) {
+      this.throw('invalid event name: ' + eventName);
+    }
+
+    this.debug('_emitEvent:' + eventName + ' ' + value);
+    var eventObj = {
+      type: eventName,
+      detail: value
+    };
+    listeners.forEach((listener) => {
+      listener.call(this, eventObj);
+    });
+  };
+
+  /**
+   * Add an event listener on an event. If listener is an object,
+   * object.handleEvent is called when the event emits.
+   *
+   * @access public
+   * @memberOf EventEmitter.prototype
+   * @param {String} eventName
+   * @param {(Function|Object)} listener
+   */
+  EventEmitter.prototype.addEventListener = function(eventName, listener) {
+    var listeners = this._eventListeners[eventName];
+    if (listener && listeners) {
+      switch (typeof listener) {
+        case 'function':
+          break;
+        case 'object':
+          if (typeof listener.handleEvent === 'function') {
+            listener = listener.handleEvent;
+          } else {
+            listener = null;
+          }
+          break;
+        default:
+          listener = null;
+          break;
+      }
+      if (listener && listeners.indexOf(listener) < 0) {
+        listeners.push(listener);
+      } 
+    } else {
+      this.error('addEventListener: invalid listener for ' + eventName);
+    }
+  };
+
+  /**
+   * Remove the event listener from an event.
+   *
+   * @access public
+   * @memberOf EventEmitter.prototype
+   * @param {String} eventName
+   * @param {(Function|Object)} listener
+   */
+  EventEmitter.prototype.removeEventListener = function(eventName, listener) {
+    var listeners = this._eventListeners[eventName];
+    if (listener && listeners) {
+      var index = -1;
+      var type = typeof listener;
+      switch (type) {
+        case 'function':
+          index = listeners.indexOf(listener);
+          break;
+        case 'object':
+          index = listeners.indexOf(listener.handleEvent);
+          break;
+      }
+      if (index >= 0) {
+        listeners.splice(index, 1);
+      }
+    } else {
+      this.error('removeEventListener: invalid listener for ' + eventName);
+    }
+  };
+
+  return EventEmitter;
+});