latency-monitor/dist/VisibilityChangeEmitter.js

A generic latency monitor for node/browers

'use strict';

Object.defineProperty(exports, "__esModule", {
    value: true
});

var _createClass = function () { function defineProperties(target, props) { for (var i = 0; i < props.length; i++) { var descriptor = props[i]; descriptor.enumerable = descriptor.enumerable || false; descriptor.configurable = true; if ("value" in descriptor) descriptor.writable = true; Object.defineProperty(target, descriptor.key, descriptor); } } return function (Constructor, protoProps, staticProps) { if (protoProps) defineProperties(Constructor.prototype, protoProps); if (staticProps) defineProperties(Constructor, staticProps); return Constructor; }; }();

var _events = require('events');

var _events2 = _interopRequireDefault(_events);

function _interopRequireDefault(obj) { return obj && obj.__esModule ? obj : { default: obj }; }

function _classCallCheck(instance, Constructor) { if (!(instance instanceof Constructor)) { throw new TypeError("Cannot call a class as a function"); } }

function _possibleConstructorReturn(self, call) { if (!self) { throw new ReferenceError("this hasn't been initialised - super() hasn't been called"); } return call && (typeof call === "object" || typeof call === "function") ? call : self; }

function _inherits(subClass, superClass) { if (typeof superClass !== "function" && superClass !== null) { throw new TypeError("Super expression must either be null or a function, not " + typeof superClass); } subClass.prototype = Object.create(superClass && superClass.prototype, { constructor: { value: subClass, enumerable: false, writable: true, configurable: true } }); if (superClass) Object.setPrototypeOf ? Object.setPrototypeOf(subClass, superClass) : subClass.__proto__ = superClass; } /* global document */

var debug = require('debug')('latency-monitor:VisibilityChangeEmitter');

/**
 * Listen to page visibility change events (i.e. when the page is focused / blurred) by an event emitter.
 *
 * Warning: This does not work on all browsers, but should work on all modern browsers
 *
 * @example
 *
 *     const myVisibilityEmitter = new VisibilityChangeEmitter();
 *
 *     myVisibilityEmitter.on('visibilityChange', (pageInFocus) => {
 *        if ( pageInFocus ){
 *            // Page is in focus
 *            console.log('In focus');
 *        }
 *        else {
 *            // Page is blurred
 *            console.log('Out of focus');
 *        }
 *     });
 *     // To access the visibility state directly, call:
 *     console.log('Am I focused now? ' + myVisibilityEmitter.isVisible());
 *
 * @class VisibilityChangeEmitter
 */

var VisibilityChangeEmitter = function (_EventEmitter) {
    _inherits(VisibilityChangeEmitter, _EventEmitter);

    /**
     * Creates a VisibilityChangeEmitter
     */
    function VisibilityChangeEmitter() {
        _classCallCheck(this, VisibilityChangeEmitter);

        var _this = _possibleConstructorReturn(this, (VisibilityChangeEmitter.__proto__ || Object.getPrototypeOf(VisibilityChangeEmitter)).call(this));

        if (typeof document === 'undefined') {
            debug('This is not a browser, no "document" found. Stopping.');
            return _possibleConstructorReturn(_this);
        }
        _this._initializeVisibilityVarNames();
        _this._addVisibilityChangeListener();
        return _this;
    }

    /**
     * document.hidden and document.visibilityChange are the two variables we need to check for;
     * Since these variables are named differently in different browsers, this function sets
     * the appropriate name based on the browser being used. Once executed, tha actual names of
     * document.hidden and document.visibilityChange are found in this._hidden and this._visibilityChange
     * respectively
     * @private
     */


    _createClass(VisibilityChangeEmitter, [{
        key: '_initializeVisibilityVarNames',
        value: function _initializeVisibilityVarNames() {
            var hidden = void 0;
            var visibilityChange = void 0;
            if (typeof document.hidden !== 'undefined') {
                // Opera 12.10 and Firefox 18 and later support
                hidden = 'hidden';
                visibilityChange = 'visibilitychange';
            } else if (typeof document.mozHidden !== 'undefined') {
                hidden = 'mozHidden';
                visibilityChange = 'mozvisibilitychange';
            } else if (typeof document.msHidden !== 'undefined') {
                hidden = 'msHidden';
                visibilityChange = 'msvisibilitychange';
            } else if (typeof document.webkitHidden !== 'undefined') {
                hidden = 'webkitHidden';
                visibilityChange = 'webkitvisibilitychange';
            }
            this._hidden = hidden;
            this._visibilityChange = visibilityChange;
        }

        /**
         * Adds an event listener on the document that listens to changes in document.visibilityChange
         * (or whatever name by which the visibilityChange variable is known in the browser)
         * @private
         */

    }, {
        key: '_addVisibilityChangeListener',
        value: function _addVisibilityChangeListener() {
            if (typeof document.addEventListener === 'undefined' || typeof document[this._hidden] === 'undefined') {
                debug('Checking page visibility requires a browser that supports the Page Visibility API.');
            } else {
                // Handle page visibility change
                document.addEventListener(this._visibilityChange, this._handleVisibilityChange.bind(this), false);
            }
        }

        /**
         * The function returns ```true``` if the page is visible or ```false``` if the page is not visible and
         * ```undefined``` if the page visibility API is not supported by the browser.
         * @returns {Boolean|void} whether the page is now visible or not (undefined is unknown)
         */

    }, {
        key: 'isVisible',
        value: function isVisible() {
            if (this._hidden === undefined || document[this._hidden] === undefined) {
                return undefined;
            }

            return !document[this._hidden];
        }

        /**
         * The function that is called when document.visibilityChange has changed
         * It emits an event called visibilityChange and sends the value of document.hidden as a
         * parameter
         *
         * @private
         */

    }, {
        key: '_handleVisibilityChange',
        value: function _handleVisibilityChange() {
            var visible = !document[this._hidden];
            debug(visible ? 'Page Visible' : 'Page Hidden');
            // Emit the event
            this.emit('visibilityChange', visible);
        }
    }]);

    return VisibilityChangeEmitter;
}(_events2.default);

exports.default = VisibilityChangeEmitter;
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