visibilityApi.js

Handles cross-browser tab visibility events

• ¶

  /* This Source Code Form is subject to the terms of the Mozilla Public
   * License, v. 2.0. If a copy of the MPL was not distributed with this file,
   * You can obtain one at http://mozilla.org/MPL/2.0/. */
  
  /* Loading this module will cause, when TogetherJS is active, the
     session object to emit visibility-change with a `hidden` argument
     whenever the visibility changes, on browsers where we can detect
     it.
     */
  
  define(["util", "session"], function (util, session) {
    var visibilityApi = util.Module("visibilityApi");
    var hidden;
    var visibilityChange;
    if (document.hidden !== undefined) { // Opera 12.10 and Firefox 18 and later support
      hidden = "hidden";
      visibilityChange = "visibilitychange";
    } else if (document.mozHidden !== undefined) {
      hidden = "mozHidden";
      visibilityChange = "mozvisibilitychange";
    } else if (document.msHidden !== undefined) {
      hidden = "msHidden";
      visibilityChange = "msvisibilitychange";
    } else if (document.webkitHidden !== undefined) {
      hidden = "webkitHidden";
      visibilityChange = "webkitvisibilitychange";
    }
  
    session.on("start", function () {
      document.addEventListener(visibilityChange, change, false);
    });
  
    session.on("close", function () {
      document.removeEventListener(visibilityChange, change, false);
    });
  
    function change() {
      session.emit("visibility-change", document[hidden]);
    }
  
    visibilityApi.hidden = function () {
      return document[hidden];
    };
  
    return visibilityApi;
  });