Subscribable.js

/**
 * Copyright (c) 2015, Facebook, Inc.  All rights reserved.
 *
 * Facebook, Inc. ("Facebook") owns all right, title and interest, including
 * all intellectual property and other proprietary rights, in and to the React
 * Native CustomComponents software (the "Software").  Subject to your
 * compliance with these terms, you are hereby granted a non-exclusive,
 * worldwide, royalty-free copyright license to (1) use and copy the Software;
 * and (2) reproduce and distribute the Software as part of your own software
 * ("Your Software").  Facebook reserves all rights not expressly granted to
 * you in this license agreement.
 *
 * THE SOFTWARE AND DOCUMENTATION, IF ANY, ARE PROVIDED "AS IS" AND ANY EXPRESS
 * OR IMPLIED WARRANTIES (INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE) ARE DISCLAIMED.
 * IN NO EVENT SHALL FACEBOOK OR ITS AFFILIATES, OFFICERS, DIRECTORS OR
 * EMPLOYEES BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
 * OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
 * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
 * OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THE SOFTWARE, EVEN IF
 * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 * @flow
 */
'use strict';

import type EventEmitter from './EventEmitter';

/**
 * Subscribable provides a mixin for safely subscribing a component to an
 * eventEmitter
 *
 * This will be replaced with the observe interface that will be coming soon to
 * React Core
 */

var Subscribable = {};

Subscribable.Mixin = {

  componentWillMount: function() {
    this._subscribableSubscriptions = [];
  },

  componentWillUnmount: function() {
    this._subscribableSubscriptions.forEach(
      (subscription) => subscription.remove()
    );
    this._subscribableSubscriptions = null;
  },

  /**
   * Special form of calling `addListener` that *guarantees* that a
   * subscription *must* be tied to a component instance, and therefore will
   * be cleaned up when the component is unmounted. It is impossible to create
   * the subscription and pass it in - this method must be the one to create
   * the subscription and therefore can guarantee it is retained in a way that
   * will be cleaned up.
   *
   * @param {EventEmitter} eventEmitter emitter to subscribe to.
   * @param {string} eventType Type of event to listen to.
   * @param {function} listener Function to invoke when event occurs.
   * @param {object} context Object to use as listener context.
   */
  addListenerOn: function(
    eventEmitter: EventEmitter,
    eventType: string,
    listener: Function,
    context: Object
  ) {
    this._subscribableSubscriptions.push(
      eventEmitter.addListener(eventType, listener, context)
    );
  }
};

module.exports = Subscribable;