balmet.com

heartbeat.js (23140B)

---

 /**
  * Heartbeat API
  *
  * Heartbeat is a simple server polling API that sends XHR requests to
  * the server every 15 - 60 seconds and triggers events (or callbacks) upon
  * receiving data. Currently these 'ticks' handle transports for post locking,
  * login-expiration warnings, autosave, and related tasks while a user is logged in.
  *
  * Available PHP filters (in ajax-actions.php):
  * - heartbeat_received
  * - heartbeat_send
  * - heartbeat_tick
  * - heartbeat_nopriv_received
  * - heartbeat_nopriv_send
  * - heartbeat_nopriv_tick
  * @see wp_ajax_nopriv_heartbeat(), wp_ajax_heartbeat()
  *
  * Custom jQuery events:
  * - heartbeat-send
  * - heartbeat-tick
  * - heartbeat-error
  * - heartbeat-connection-lost
  * - heartbeat-connection-restored
  * - heartbeat-nonces-expired
  *
  * @since 3.6.0
  * @output wp-includes/js/heartbeat.js
  */
 
 ( function( $, window, undefined ) {
 
 	/**
 	 * Constructs the Heartbeat API.
 	 *
 	 * @since 3.6.0
 	 *
 	 * @return {Object} An instance of the Heartbeat class.
 	 * @constructor
 	 */
 	var Heartbeat = function() {
 		var $document = $(document),
 			settings = {
 				// Suspend/resume.
 				suspend: false,
 
 				// Whether suspending is enabled.
 				suspendEnabled: true,
 
 				// Current screen id, defaults to the JS global 'pagenow' when present
 				// (in the admin) or 'front'.
 				screenId: '',
 
 				// XHR request URL, defaults to the JS global 'ajaxurl' when present.
 				url: '',
 
 				// Timestamp, start of the last connection request.
 				lastTick: 0,
 
 				// Container for the enqueued items.
 				queue: {},
 
 				// Connect interval (in seconds).
 				mainInterval: 60,
 
 				// Used when the interval is set to 5 seconds temporarily.
 				tempInterval: 0,
 
 				// Used when the interval is reset.
 				originalInterval: 0,
 
 				// Used to limit the number of Ajax requests.
 				minimalInterval: 0,
 
 				// Used together with tempInterval.
 				countdown: 0,
 
 				// Whether a connection is currently in progress.
 				connecting: false,
 
 				// Whether a connection error occurred.
 				connectionError: false,
 
 				// Used to track non-critical errors.
 				errorcount: 0,
 
 				// Whether at least one connection has been completed successfully.
 				hasConnected: false,
 
 				// Whether the current browser window is in focus and the user is active.
 				hasFocus: true,
 
 				// Timestamp, last time the user was active. Checked every 30 seconds.
 				userActivity: 0,
 
 				// Flag whether events tracking user activity were set.
 				userActivityEvents: false,
 
 				// Timer that keeps track of how long a user has focus.
 				checkFocusTimer: 0,
 
 				// Timer that keeps track of how long needs to be waited before connecting to
 				// the server again.
 				beatTimer: 0
 			};
 
 		/**
 		 * Sets local variables and events, then starts the heartbeat.
 		 *
 		 * @since 3.8.0
 		 * @access private
 		 *
 		 * @return {void}
 		 */
 		function initialize() {
 			var options, hidden, visibilityState, visibilitychange;
 
 			if ( typeof window.pagenow === 'string' ) {
 				settings.screenId = window.pagenow;
 			}
 
 			if ( typeof window.ajaxurl === 'string' ) {
 				settings.url = window.ajaxurl;
 			}
 
 			// Pull in options passed from PHP.
 			if ( typeof window.heartbeatSettings === 'object' ) {
 				options = window.heartbeatSettings;
 
 				// The XHR URL can be passed as option when window.ajaxurl is not set.
 				if ( ! settings.url && options.ajaxurl ) {
 					settings.url = options.ajaxurl;
 				}
 
 				/*
 				 * The interval can be from 15 to 120 seconds and can be set temporarily to 5 seconds.
 				 * It can be set in the initial options or changed later through JS and/or through PHP.
 				 */
 				if ( options.interval ) {
 					settings.mainInterval = options.interval;
 
 					if ( settings.mainInterval < 15 ) {
 						settings.mainInterval = 15;
 					} else if ( settings.mainInterval > 120 ) {
 						settings.mainInterval = 120;
 					}
 				}
 
 				/*
 				 * Used to limit the number of Ajax requests. Overrides all other intervals
 				 * if they are shorter. Needed for some hosts that cannot handle frequent requests
 				 * and the user may exceed the allocated server CPU time, etc. The minimal interval
 				 * can be up to 600 seconds, however setting it to longer than 120 seconds
 				 * will limit or disable some of the functionality (like post locks).
 				 * Once set at initialization, minimalInterval cannot be changed/overridden.
 				 */
 				if ( options.minimalInterval ) {
 					options.minimalInterval = parseInt( options.minimalInterval, 10 );
 					settings.minimalInterval = options.minimalInterval > 0 && options.minimalInterval <= 600 ? options.minimalInterval * 1000 : 0;
 				}
 
 				if ( settings.minimalInterval && settings.mainInterval < settings.minimalInterval ) {
 					settings.mainInterval = settings.minimalInterval;
 				}
 
 				// 'screenId' can be added from settings on the front end where the JS global
 				// 'pagenow' is not set.
 				if ( ! settings.screenId ) {
 					settings.screenId = options.screenId || 'front';
 				}
 
 				if ( options.suspension === 'disable' ) {
 					settings.suspendEnabled = false;
 				}
 			}
 
 			// Convert to milliseconds.
 			settings.mainInterval = settings.mainInterval * 1000;
 			settings.originalInterval = settings.mainInterval;
 
 			/*
 			 * Switch the interval to 120 seconds by using the Page Visibility API.
 			 * If the browser doesn't support it (Safari < 7, Android < 4.4, IE < 10), the
 			 * interval will be increased to 120 seconds after 5 minutes of mouse and keyboard
 			 * inactivity.
 			 */
 			if ( typeof document.hidden !== 'undefined' ) {
 				hidden = 'hidden';
 				visibilitychange = 'visibilitychange';
 				visibilityState = 'visibilityState';
 			} else if ( typeof document.msHidden !== 'undefined' ) { // IE10.
 				hidden = 'msHidden';
 				visibilitychange = 'msvisibilitychange';
 				visibilityState = 'msVisibilityState';
 			} else if ( typeof document.webkitHidden !== 'undefined' ) { // Android.
 				hidden = 'webkitHidden';
 				visibilitychange = 'webkitvisibilitychange';
 				visibilityState = 'webkitVisibilityState';
 			}
 
 			if ( hidden ) {
 				if ( document[hidden] ) {
 					settings.hasFocus = false;
 				}
 
 				$document.on( visibilitychange + '.wp-heartbeat', function() {
 					if ( document[visibilityState] === 'hidden' ) {
 						blurred();
 						window.clearInterval( settings.checkFocusTimer );
 					} else {
 						focused();
 						if ( document.hasFocus ) {
 							settings.checkFocusTimer = window.setInterval( checkFocus, 10000 );
 						}
 					}
 				});
 			}
 
 			// Use document.hasFocus() if available.
 			if ( document.hasFocus ) {
 				settings.checkFocusTimer = window.setInterval( checkFocus, 10000 );
 			}
 
 			$(window).on( 'unload.wp-heartbeat', function() {
 				// Don't connect anymore.
 				settings.suspend = true;
 
 				// Abort the last request if not completed.
 				if ( settings.xhr && settings.xhr.readyState !== 4 ) {
 					settings.xhr.abort();
 				}
 			});
 
 			// Check for user activity every 30 seconds.
 			window.setInterval( checkUserActivity, 30000 );
 
 			// Start one tick after DOM ready.
 			$( function() {
 				settings.lastTick = time();
 				scheduleNextTick();
 			});
 		}
 
 		/**
 		 * Returns the current time according to the browser.
 		 *
 		 * @since 3.6.0
 		 * @access private
 		 *
 		 * @return {number} Returns the current time.
 		 */
 		function time() {
 			return (new Date()).getTime();
 		}
 
 		/**
 		 * Checks if the iframe is from the same origin.
 		 *
 		 * @since 3.6.0
 		 * @access private
 		 *
 		 * @return {boolean} Returns whether or not the iframe is from the same origin.
 		 */
 		function isLocalFrame( frame ) {
 			var origin, src = frame.src;
 
 			/*
 			 * Need to compare strings as WebKit doesn't throw JS errors when iframes have
 			 * different origin. It throws uncatchable exceptions.
 			 */
 			if ( src && /^https?:\/\//.test( src ) ) {
 				origin = window.location.origin ? window.location.origin : window.location.protocol + '//' + window.location.host;
 
 				if ( src.indexOf( origin ) !== 0 ) {
 					return false;
 				}
 			}
 
 			try {
 				if ( frame.contentWindow.document ) {
 					return true;
 				}
 			} catch(e) {}
 
 			return false;
 		}
 
 		/**
 		 * Checks if the document's focus has changed.
 		 *
 		 * @since 4.1.0
 		 * @access private
 		 *
 		 * @return {void}
 		 */
 		function checkFocus() {
 			if ( settings.hasFocus && ! document.hasFocus() ) {
 				blurred();
 			} else if ( ! settings.hasFocus && document.hasFocus() ) {
 				focused();
 			}
 		}
 
 		/**
 		 * Sets error state and fires an event on XHR errors or timeout.
 		 *
 		 * @since 3.8.0
 		 * @access private
 		 *
 		 * @param {string} error  The error type passed from the XHR.
 		 * @param {number} status The HTTP status code passed from jqXHR
 		 *                        (200, 404, 500, etc.).
 		 *
 		 * @return {void}
 		 */
 		function setErrorState( error, status ) {
 			var trigger;
 
 			if ( error ) {
 				switch ( error ) {
 					case 'abort':
 						// Do nothing.
 						break;
 					case 'timeout':
 						// No response for 30 seconds.
 						trigger = true;
 						break;
 					case 'error':
 						if ( 503 === status && settings.hasConnected ) {
 							trigger = true;
 							break;
 						}
 						/* falls through */
 					case 'parsererror':
 					case 'empty':
 					case 'unknown':
 						settings.errorcount++;
 
 						if ( settings.errorcount > 2 && settings.hasConnected ) {
 							trigger = true;
 						}
 
 						break;
 				}
 
 				if ( trigger && ! hasConnectionError() ) {
 					settings.connectionError = true;
 					$document.trigger( 'heartbeat-connection-lost', [error, status] );
 					wp.hooks.doAction( 'heartbeat.connection-lost', error, status );
 				}
 			}
 		}
 
 		/**
 		 * Clears the error state and fires an event if there is a connection error.
 		 *
 		 * @since 3.8.0
 		 * @access private
 		 *
 		 * @return {void}
 		 */
 		function clearErrorState() {
 			// Has connected successfully.
 			settings.hasConnected = true;
 
 			if ( hasConnectionError() ) {
 				settings.errorcount = 0;
 				settings.connectionError = false;
 				$document.trigger( 'heartbeat-connection-restored' );
 				wp.hooks.doAction( 'heartbeat.connection-restored' );
 			}
 		}
 
 		/**
 		 * Gathers the data and connects to the server.
 		 *
 		 * @since 3.6.0
 		 * @access private
 		 *
 		 * @return {void}
 		 */
 		function connect() {
 			var ajaxData, heartbeatData;
 
 			// If the connection to the server is slower than the interval,
 			// heartbeat connects as soon as the previous connection's response is received.
 			if ( settings.connecting || settings.suspend ) {
 				return;
 			}
 
 			settings.lastTick = time();
 
 			heartbeatData = $.extend( {}, settings.queue );
 			// Clear the data queue. Anything added after this point will be sent on the next tick.
 			settings.queue = {};
 
 			$document.trigger( 'heartbeat-send', [ heartbeatData ] );
 			wp.hooks.doAction( 'heartbeat.send', heartbeatData );
 
 			ajaxData = {
 				data: heartbeatData,
 				interval: settings.tempInterval ? settings.tempInterval / 1000 : settings.mainInterval / 1000,
 				_nonce: typeof window.heartbeatSettings === 'object' ? window.heartbeatSettings.nonce : '',
 				action: 'heartbeat',
 				screen_id: settings.screenId,
 				has_focus: settings.hasFocus
 			};
 
 			if ( 'customize' === settings.screenId  ) {
 				ajaxData.wp_customize = 'on';
 			}
 
 			settings.connecting = true;
 			settings.xhr = $.ajax({
 				url: settings.url,
 				type: 'post',
 				timeout: 30000, // Throw an error if not completed after 30 seconds.
 				data: ajaxData,
 				dataType: 'json'
 			}).always( function() {
 				settings.connecting = false;
 				scheduleNextTick();
 			}).done( function( response, textStatus, jqXHR ) {
 				var newInterval;
 
 				if ( ! response ) {
 					setErrorState( 'empty' );
 					return;
 				}
 
 				clearErrorState();
 
 				if ( response.nonces_expired ) {
 					$document.trigger( 'heartbeat-nonces-expired' );
 					wp.hooks.doAction( 'heartbeat.nonces-expired' );
 				}
 
 				// Change the interval from PHP.
 				if ( response.heartbeat_interval ) {
 					newInterval = response.heartbeat_interval;
 					delete response.heartbeat_interval;
 				}
 
 				// Update the heartbeat nonce if set.
 				if ( response.heartbeat_nonce && typeof window.heartbeatSettings === 'object' ) {
 					window.heartbeatSettings.nonce = response.heartbeat_nonce;
 					delete response.heartbeat_nonce;
 				}
 
 				// Update the Rest API nonce if set and wp-api loaded.
 				if ( response.rest_nonce && typeof window.wpApiSettings === 'object' ) {
 					window.wpApiSettings.nonce = response.rest_nonce;
 					// This nonce is required for api-fetch through heartbeat.tick.
 					// delete response.rest_nonce;
 				}
 
 				$document.trigger( 'heartbeat-tick', [response, textStatus, jqXHR] );
 				wp.hooks.doAction( 'heartbeat.tick', response, textStatus, jqXHR );
 
 				// Do this last. Can trigger the next XHR if connection time > 5 seconds and newInterval == 'fast'.
 				if ( newInterval ) {
 					interval( newInterval );
 				}
 			}).fail( function( jqXHR, textStatus, error ) {
 				setErrorState( textStatus || 'unknown', jqXHR.status );
 				$document.trigger( 'heartbeat-error', [jqXHR, textStatus, error] );
 				wp.hooks.doAction( 'heartbeat.error', jqXHR, textStatus, error );
 			});
 		}
 
 		/**
 		 * Schedules the next connection.
 		 *
 		 * Fires immediately if the connection time is longer than the interval.
 		 *
 		 * @since 3.8.0
 		 * @access private
 		 *
 		 * @return {void}
 		 */
 		function scheduleNextTick() {
 			var delta = time() - settings.lastTick,
 				interval = settings.mainInterval;
 
 			if ( settings.suspend ) {
 				return;
 			}
 
 			if ( ! settings.hasFocus ) {
 				interval = 120000; // 120 seconds. Post locks expire after 150 seconds.
 			} else if ( settings.countdown > 0 && settings.tempInterval ) {
 				interval = settings.tempInterval;
 				settings.countdown--;
 
 				if ( settings.countdown < 1 ) {
 					settings.tempInterval = 0;
 				}
 			}
 
 			if ( settings.minimalInterval && interval < settings.minimalInterval ) {
 				interval = settings.minimalInterval;
 			}
 
 			window.clearTimeout( settings.beatTimer );
 
 			if ( delta < interval ) {
 				settings.beatTimer = window.setTimeout(
 					function() {
 						connect();
 					},
 					interval - delta
 				);
 			} else {
 				connect();
 			}
 		}
 
 		/**
 		 * Sets the internal state when the browser window becomes hidden or loses focus.
 		 *
 		 * @since 3.6.0
 		 * @access private
 		 *
 		 * @return {void}
 		 */
 		function blurred() {
 			settings.hasFocus = false;
 		}
 
 		/**
 		 * Sets the internal state when the browser window becomes visible or is in focus.
 		 *
 		 * @since 3.6.0
 		 * @access private
 		 *
 		 * @return {void}
 		 */
 		function focused() {
 			settings.userActivity = time();
 
 			// Resume if suspended.
 			settings.suspend = false;
 
 			if ( ! settings.hasFocus ) {
 				settings.hasFocus = true;
 				scheduleNextTick();
 			}
 		}
 
 		/**
 		 * Runs when the user becomes active after a period of inactivity.
 		 *
 		 * @since 3.6.0
 		 * @access private
 		 *
 		 * @return {void}
 		 */
 		function userIsActive() {
 			settings.userActivityEvents = false;
 			$document.off( '.wp-heartbeat-active' );
 
 			$('iframe').each( function( i, frame ) {
 				if ( isLocalFrame( frame ) ) {
 					$( frame.contentWindow ).off( '.wp-heartbeat-active' );
 				}
 			});
 
 			focused();
 		}
 
 		/**
 		 * Checks for user activity.
 		 *
 		 * Runs every 30 seconds. Sets 'hasFocus = true' if user is active and the window
 		 * is in the background. Sets 'hasFocus = false' if the user has been inactive
 		 * (no mouse or keyboard activity) for 5 minutes even when the window has focus.
 		 *
 		 * @since 3.8.0
 		 * @access private
 		 *
 		 * @return {void}
 		 */
 		function checkUserActivity() {
 			var lastActive = settings.userActivity ? time() - settings.userActivity : 0;
 
 			// Throttle down when no mouse or keyboard activity for 5 minutes.
 			if ( lastActive > 300000 && settings.hasFocus ) {
 				blurred();
 			}
 
 			// Suspend after 10 minutes of inactivity when suspending is enabled.
 			// Always suspend after 60 minutes of inactivity. This will release the post lock, etc.
 			if ( ( settings.suspendEnabled && lastActive > 600000 ) || lastActive > 3600000 ) {
 				settings.suspend = true;
 			}
 
 			if ( ! settings.userActivityEvents ) {
 				$document.on( 'mouseover.wp-heartbeat-active keyup.wp-heartbeat-active touchend.wp-heartbeat-active', function() {
 					userIsActive();
 				});
 
 				$('iframe').each( function( i, frame ) {
 					if ( isLocalFrame( frame ) ) {
 						$( frame.contentWindow ).on( 'mouseover.wp-heartbeat-active keyup.wp-heartbeat-active touchend.wp-heartbeat-active', function() {
 							userIsActive();
 						});
 					}
 				});
 
 				settings.userActivityEvents = true;
 			}
 		}
 
 		// Public methods.
 
 		/**
 		 * Checks whether the window (or any local iframe in it) has focus, or the user
 		 * is active.
 		 *
 		 * @since 3.6.0
 		 * @memberOf wp.heartbeat.prototype
 		 *
 		 * @return {boolean} True if the window or the user is active.
 		 */
 		function hasFocus() {
 			return settings.hasFocus;
 		}
 
 		/**
 		 * Checks whether there is a connection error.
 		 *
 		 * @since 3.6.0
 		 *
 		 * @memberOf wp.heartbeat.prototype
 		 *
 		 * @return {boolean} True if a connection error was found.
 		 */
 		function hasConnectionError() {
 			return settings.connectionError;
 		}
 
 		/**
 		 * Connects as soon as possible regardless of 'hasFocus' state.
 		 *
 		 * Will not open two concurrent connections. If a connection is in progress,
 		 * will connect again immediately after the current connection completes.
 		 *
 		 * @since 3.8.0
 		 *
 		 * @memberOf wp.heartbeat.prototype
 		 *
 		 * @return {void}
 		 */
 		function connectNow() {
 			settings.lastTick = 0;
 			scheduleNextTick();
 		}
 
 		/**
 		 * Disables suspending.
 		 *
 		 * Should be used only when Heartbeat is performing critical tasks like
 		 * autosave, post-locking, etc. Using this on many screens may overload
 		 * the user's hosting account if several browser windows/tabs are left open
 		 * for a long time.
 		 *
 		 * @since 3.8.0
 		 *
 		 * @memberOf wp.heartbeat.prototype
 		 *
 		 * @return {void}
 		 */
 		function disableSuspend() {
 			settings.suspendEnabled = false;
 		}
 
 		/**
 		 * Gets/Sets the interval.
 		 *
 		 * When setting to 'fast' or 5, the interval is 5 seconds for the next 30 ticks
 		 * (for 2 minutes and 30 seconds) by default. In this case the number of 'ticks'
 		 * can be passed as second argument. If the window doesn't have focus,
 		 * the interval slows down to 2 minutes.
 		 *
 		 * @since 3.6.0
 		 *
 		 * @memberOf wp.heartbeat.prototype
 		 *
 		 * @param {string|number} speed Interval: 'fast' or 5, 15, 30, 60, 120.
 		 *                              Fast equals 5.
 		 * @param {string}        ticks Tells how many ticks before the interval reverts
 		 *                              back. Used with speed = 'fast' or 5.
 		 *
 		 * @return {number} Current interval in seconds.
 		 */
 		function interval( speed, ticks ) {
 			var newInterval,
 				oldInterval = settings.tempInterval ? settings.tempInterval : settings.mainInterval;
 
 			if ( speed ) {
 				switch ( speed ) {
 					case 'fast':
 					case 5:
 						newInterval = 5000;
 						break;
 					case 15:
 						newInterval = 15000;
 						break;
 					case 30:
 						newInterval = 30000;
 						break;
 					case 60:
 						newInterval = 60000;
 						break;
 					case 120:
 						newInterval = 120000;
 						break;
 					case 'long-polling':
 						// Allow long polling (experimental).
 						settings.mainInterval = 0;
 						return 0;
 					default:
 						newInterval = settings.originalInterval;
 				}
 
 				if ( settings.minimalInterval && newInterval < settings.minimalInterval ) {
 					newInterval = settings.minimalInterval;
 				}
 
 				if ( 5000 === newInterval ) {
 					ticks = parseInt( ticks, 10 ) || 30;
 					ticks = ticks < 1 || ticks > 30 ? 30 : ticks;
 
 					settings.countdown = ticks;
 					settings.tempInterval = newInterval;
 				} else {
 					settings.countdown = 0;
 					settings.tempInterval = 0;
 					settings.mainInterval = newInterval;
 				}
 
 				/*
 				 * Change the next connection time if new interval has been set.
 				 * Will connect immediately if the time since the last connection
 				 * is greater than the new interval.
 				 */
 				if ( newInterval !== oldInterval ) {
 					scheduleNextTick();
 				}
 			}
 
 			return settings.tempInterval ? settings.tempInterval / 1000 : settings.mainInterval / 1000;
 		}
 
 		/**
 		 * Enqueues data to send with the next XHR.
 		 *
 		 * As the data is send asynchronously, this function doesn't return the XHR
 		 * response. To see the response, use the custom jQuery event 'heartbeat-tick'
 		 * on the document, example:
 		 *		$(document).on( 'heartbeat-tick.myname', function( event, data, textStatus, jqXHR ) {
 		 *			// code
 		 *		});
 		 * If the same 'handle' is used more than once, the data is not overwritten when
 		 * the third argument is 'true'. Use `wp.heartbeat.isQueued('handle')` to see if
 		 * any data is already queued for that handle.
 		 *
 		 * @since 3.6.0
 		 *
 		 * @memberOf wp.heartbeat.prototype
 		 *
 		 * @param {string}  handle      Unique handle for the data, used in PHP to
 		 *                              receive the data.
 		 * @param {*}       data        The data to send.
 		 * @param {boolean} noOverwrite Whether to overwrite existing data in the queue.
 		 *
 		 * @return {boolean} True if the data was queued.
 		 */
 		function enqueue( handle, data, noOverwrite ) {
 			if ( handle ) {
 				if ( noOverwrite && this.isQueued( handle ) ) {
 					return false;
 				}
 
 				settings.queue[handle] = data;
 				return true;
 			}
 			return false;
 		}
 
 		/**
 		 * Checks if data with a particular handle is queued.
 		 *
 		 * @since 3.6.0
 		 *
 		 * @param {string} handle The handle for the data.
 		 *
 		 * @return {boolean} True if the data is queued with this handle.
 		 */
 		function isQueued( handle ) {
 			if ( handle ) {
 				return settings.queue.hasOwnProperty( handle );
 			}
 		}
 
 		/**
 		 * Removes data with a particular handle from the queue.
 		 *
 		 * @since 3.7.0
 		 *
 		 * @memberOf wp.heartbeat.prototype
 		 *
 		 * @param {string} handle The handle for the data.
 		 *
 		 * @return {void}
 		 */
 		function dequeue( handle ) {
 			if ( handle ) {
 				delete settings.queue[handle];
 			}
 		}
 
 		/**
 		 * Gets data that was enqueued with a particular handle.
 		 *
 		 * @since 3.7.0
 		 *
 		 * @memberOf wp.heartbeat.prototype
 		 *
 		 * @param {string} handle The handle for the data.
 		 *
 		 * @return {*} The data or undefined.
 		 */
 		function getQueuedItem( handle ) {
 			if ( handle ) {
 				return this.isQueued( handle ) ? settings.queue[handle] : undefined;
 			}
 		}
 
 		initialize();
 
 		// Expose public methods.
 		return {
 			hasFocus: hasFocus,
 			connectNow: connectNow,
 			disableSuspend: disableSuspend,
 			interval: interval,
 			hasConnectionError: hasConnectionError,
 			enqueue: enqueue,
 			dequeue: dequeue,
 			isQueued: isQueued,
 			getQueuedItem: getQueuedItem
 		};
 	};
 
 	/**
 	 * Ensure the global `wp` object exists.
 	 *
 	 * @namespace wp
 	 */
 	window.wp = window.wp || {};
 
 	/**
 	 * Contains the Heartbeat API.
 	 *
 	 * @namespace wp.heartbeat
 	 * @type {Heartbeat}
 	 */
 	window.wp.heartbeat = new Heartbeat();
 
 }( jQuery, window ));