@bigfishtv/cockpit/es/utils/windowVisible.js

/**
 * Window Visible Utility
 * @module Utilities/windowVisible
 */

var stateKey = null;
var eventKey = null;

var keys = {
  hidden: 'visibilitychange',
  webkitHidden: 'webkitvisibilitychange',
  mozHidden: 'mozvisibilitychange',
  msHidden: 'msvisibilitychange'
};

for (stateKey in keys) {
  if (stateKey in document) {
    eventKey = keys[stateKey];
    break;
  }
}

/**
 * Returns true/false if window is visible
 * @param  {Object} _window - defaults to window
 * @return {Boolean}
 */
export function windowVisible() {
  var _window = arguments.length > 0 && arguments[0] !== undefined ? arguments[0] : window;

  return !_window.document[stateKey];
}

/**
 * Adds 'visibilitychange' listener to window and binds to provided callback
 * @param  {Function} callback
 * @param  {Object} _window - defaults to window
 * @return {Function}
 */
export function onVisibilityChange(callback) {
  var _window = arguments.length > 1 && arguments[1] !== undefined ? arguments[1] : window;

  var func = function func() {
    return callback(windowVisible(_window));
  };
  _window.document.addEventListener(eventKey, func);
  return function () {
    return _window && _window.document && _window.document.removeEventListener(eventKey, func);
  };
}