1/**
  2 * Heartbeat API
  3 *
  4 * Heartbeat is a simple server polling API that sends XHR requests to
  5 * the server every 15 - 60 seconds and triggers events (or callbacks) upon
  6 * receiving data. Currently these 'ticks' handle transports for post locking,
  7 * login-expiration warnings, autosave, and related tasks while a user is logged in.
  8 *
  9 * Available PHP filters (in ajax-actions.php):
 10 * - heartbeat_received
 11 * - heartbeat_send
 12 * - heartbeat_tick
 13 * - heartbeat_nopriv_received
 14 * - heartbeat_nopriv_send
 15 * - heartbeat_nopriv_tick
 16 * @see wp_ajax_nopriv_heartbeat(), wp_ajax_heartbeat()
 17 *
 18 * Custom jQuery events:
 19 * - heartbeat-send
 20 * - heartbeat-tick
 21 * - heartbeat-error
 22 * - heartbeat-connection-lost
 23 * - heartbeat-connection-restored
 24 * - heartbeat-nonces-expired
 25 *
 26 * @since 3.6.0
 27 * @output wp-includes/js/heartbeat.js
 28 */
 29
 30( function( $, window, undefined ) {
 31
 32	/**
 33	 * Constructs the Heartbeat API.
 34	 *
 35	 * @since 3.6.0
 36	 *
 37	 * @return {Object} An instance of the Heartbeat class.
 38	 * @constructor
 39	 */
 40	var Heartbeat = function() {
 41		var $document = $(document),
 42			settings = {
 43				// Suspend/resume.
 44				suspend: false,
 45
 46				// Whether suspending is enabled.
 47				suspendEnabled: true,
 48
 49				// Current screen id, defaults to the JS global 'pagenow' when present
 50				// (in the admin) or 'front'.
 51				screenId: '',
 52
 53				// XHR request URL, defaults to the JS global 'ajaxurl' when present.
 54				url: '',
 55
 56				// Timestamp, start of the last connection request.
 57				lastTick: 0,
 58
 59				// Container for the enqueued items.
 60				queue: {},
 61
 62				// Connect interval (in seconds).
 63				mainInterval: 60,
 64
 65				// Used when the interval is set to 5 seconds temporarily.
 66				tempInterval: 0,
 67
 68				// Used when the interval is reset.
 69				originalInterval: 0,
 70
 71				// Used to limit the number of Ajax requests.
 72				minimalInterval: 0,
 73
 74				// Used together with tempInterval.
 75				countdown: 0,
 76
 77				// Whether a connection is currently in progress.
 78				connecting: false,
 79
 80				// Whether a connection error occurred.
 81				connectionError: false,
 82
 83				// Used to track non-critical errors.
 84				errorcount: 0,
 85
 86				// Whether at least one connection has been completed successfully.
 87				hasConnected: false,
 88
 89				// Whether the current browser window is in focus and the user is active.
 90				hasFocus: true,
 91
 92				// Timestamp, last time the user was active. Checked every 30 seconds.
 93				userActivity: 0,
 94
 95				// Flag whether events tracking user activity were set.
 96				userActivityEvents: false,
 97
 98				// Timer that keeps track of how long a user has focus.
 99				checkFocusTimer: 0,
100
101				// Timer that keeps track of how long needs to be waited before connecting to
102				// the server again.
103				beatTimer: 0
104			};
105
106		/**
107		 * Sets local variables and events, then starts the heartbeat.
108		 *
109		 * @since 3.8.0
110		 * @access private
111		 *
112		 * @return {void}
113		 */
114		function initialize() {
115			var options, hidden, visibilityState, visibilitychange;
116
117			if ( typeof window.pagenow === 'string' ) {
118				settings.screenId = window.pagenow;
119			}
120
121			if ( typeof window.ajaxurl === 'string' ) {
122				settings.url = window.ajaxurl;
123			}
124
125			// Pull in options passed from PHP.
126			if ( typeof window.heartbeatSettings === 'object' ) {
127				options = window.heartbeatSettings;
128
129				// The XHR URL can be passed as option when window.ajaxurl is not set.
130				if ( ! settings.url && options.ajaxurl ) {
131					settings.url = options.ajaxurl;
132				}
133
134				/*
135				 * Logic check: the interval can be from 1 to 3600 seconds and can be set temporarily
136				 * to 5 seconds. It can be set in the initial options or changed later from JS
137				 * or from PHP through the AJAX responses.
138				 */
139				if ( options.interval ) {
140					settings.mainInterval = options.interval;
141
142					if ( settings.mainInterval < 1 ) {
143						settings.mainInterval = 1;
144					} else if ( settings.mainInterval > 3600 ) {
145						settings.mainInterval = 3600;
146					}
147				}
148
149				/*
150				 * Used to limit the number of Ajax requests. Overrides all other intervals
151				 * if they are shorter. Needed for some hosts that cannot handle frequent requests
152				 * and the user may exceed the allocated server CPU time, etc. The minimal interval
153				 * can be up to 600 seconds, however setting it to longer than 120 seconds
154				 * will limit or disable some of the functionality (like post locks).
155				 * Once set at initialization, minimalInterval cannot be changed/overridden.
156				 */
157				if ( options.minimalInterval ) {
158					options.minimalInterval = parseInt( options.minimalInterval, 10 );
159					settings.minimalInterval = options.minimalInterval > 0 && options.minimalInterval <= 600 ? options.minimalInterval : 0;
160				}
161
162				if ( settings.minimalInterval && settings.mainInterval < settings.minimalInterval ) {
163					settings.mainInterval = settings.minimalInterval;
164				}
165
166				// 'screenId' can be added from settings on the front end where the JS global
167				// 'pagenow' is not set.
168				if ( ! settings.screenId ) {
169					settings.screenId = options.screenId || 'front';
170				}
171
172				if ( options.suspension === 'disable' ) {
173					settings.suspendEnabled = false;
174				}
175			}
176
177			// Convert to milliseconds.
178			settings.mainInterval = settings.mainInterval * 1000;
179			settings.originalInterval = settings.mainInterval;
180			if ( settings.minimalInterval ) {
181				settings.minimalInterval = settings.minimalInterval * 1000;
182			}
183
184			/*
185			 * Switch the interval to 120 seconds by using the Page Visibility API.
186			 * If the browser doesn't support it (Safari < 7, Android < 4.4, IE < 10), the
187			 * interval will be increased to 120 seconds after 5 minutes of mouse and keyboard
188			 * inactivity.
189			 */
190			if ( typeof document.hidden !== 'undefined' ) {
191				hidden = 'hidden';
192				visibilitychange = 'visibilitychange';
193				visibilityState = 'visibilityState';
194			} else if ( typeof document.msHidden !== 'undefined' ) { // IE10.
195				hidden = 'msHidden';
196				visibilitychange = 'msvisibilitychange';
197				visibilityState = 'msVisibilityState';
198			} else if ( typeof document.webkitHidden !== 'undefined' ) { // Android.
199				hidden = 'webkitHidden';
200				visibilitychange = 'webkitvisibilitychange';
201				visibilityState = 'webkitVisibilityState';
202			}
203
204			if ( hidden ) {
205				if ( document[hidden] ) {
206					settings.hasFocus = false;
207				}
208
209				$document.on( visibilitychange + '.wp-heartbeat', function() {
210					if ( document[visibilityState] === 'hidden' ) {
211						blurred();
212						window.clearInterval( settings.checkFocusTimer );
213					} else {
214						focused();
215						if ( document.hasFocus ) {
216							settings.checkFocusTimer = window.setInterval( checkFocus, 10000 );
217						}
218					}
219				});
220			}
221
222			// Use document.hasFocus() if available.
223			if ( document.hasFocus ) {
224				settings.checkFocusTimer = window.setInterval( checkFocus, 10000 );
225			}
226
227			$(window).on( 'pagehide.wp-heartbeat', function() {
228				// Don't connect anymore.
229				suspend();
230
231				// Abort the last request if not completed.
232				if ( settings.xhr && settings.xhr.readyState !== 4 ) {
233					settings.xhr.abort();
234				}
235			});
236
237			$(window).on(
238				'pageshow.wp-heartbeat',
239				/**
240				 * Handles pageshow event, specifically when page navigation is restored from back/forward cache.
241				 *
242				 * @param {jQuery.Event} event
243				 * @param {PageTransitionEvent} event.originalEvent
244				 */
245				function ( event ) {
246					if ( event.originalEvent.persisted ) {
247						/*
248						 * When page navigation is stored via bfcache (Back/Forward Cache), consider this the same as
249						 * if the user had just switched to the tab since the behavior is similar.
250						 */
251						focused();
252					}
253				}
254			);
255
256			// Check for user activity every 30 seconds.
257			window.setInterval( checkUserActivity, 30000 );
258
259			// Start one tick after DOM ready.
260			$( function() {
261				settings.lastTick = time();
262				scheduleNextTick();
263			});
264		}
265
266		/**
267		 * Returns the current time according to the browser.
268		 *
269		 * @since 3.6.0
270		 * @access private
271		 *
272		 * @return {number} Returns the current time.
273		 */
274		function time() {
275			return (new Date()).getTime();
276		}
277
278		/**
279		 * Checks if the iframe is from the same origin.
280		 *
281		 * @since 3.6.0
282		 * @access private
283		 *
284		 * @return {boolean} Returns whether or not the iframe is from the same origin.
285		 */
286		function isLocalFrame( frame ) {
287			var origin, src = frame.src;
288
289			/*
290			 * Need to compare strings as WebKit doesn't throw JS errors when iframes have
291			 * different origin. It throws uncatchable exceptions.
292			 */
293			if ( src && /^https?:\/\//.test( src ) ) {
294				origin = window.location.origin ? window.location.origin : window.location.protocol + '//' + window.location.host;
295
296				if ( src.indexOf( origin ) !== 0 ) {
297					return false;
298				}
299			}
300
301			try {
302				if ( frame.contentWindow.document ) {
303					return true;
304				}
305			} catch(e) {}
306
307			return false;
308		}
309
310		/**
311		 * Checks if the document's focus has changed.
312		 *
313		 * @since 4.1.0
314		 * @access private
315		 *
316		 * @return {void}
317		 */
318		function checkFocus() {
319			if ( settings.hasFocus && ! document.hasFocus() ) {
320				blurred();
321			} else if ( ! settings.hasFocus && document.hasFocus() ) {
322				focused();
323			}
324		}
325
326		/**
327		 * Sets error state and fires an event on XHR errors or timeout.
328		 *
329		 * @since 3.8.0
330		 * @access private
331		 *
332		 * @param {string} error  The error type passed from the XHR.
333		 * @param {number} status The HTTP status code passed from jqXHR
334		 *                        (200, 404, 500, etc.).
335		 *
336		 * @return {void}
337		 */
338		function setErrorState( error, status ) {
339			var trigger;
340
341			if ( error ) {
342				switch ( error ) {
343					case 'abort':
344						// Do nothing.
345						break;
346					case 'timeout':
347						// No response for 30 seconds.
348						trigger = true;
349						break;
350					case 'error':
351						if ( 503 === status && settings.hasConnected ) {
352							trigger = true;
353							break;
354						}
355						/* falls through */
356					case 'parsererror':
357					case 'empty':
358					case 'unknown':
359						settings.errorcount++;
360
361						if ( settings.errorcount > 2 && settings.hasConnected ) {
362							trigger = true;
363						}
364
365						break;
366				}
367
368				if ( trigger && ! hasConnectionError() ) {
369					settings.connectionError = true;
370					$document.trigger( 'heartbeat-connection-lost', [error, status] );
371					wp.hooks.doAction( 'heartbeat.connection-lost', error, status );
372				}
373			}
374		}
375
376		/**
377		 * Clears the error state and fires an event if there is a connection error.
378		 *
379		 * @since 3.8.0
380		 * @access private
381		 *
382		 * @return {void}
383		 */
384		function clearErrorState() {
385			// Has connected successfully.
386			settings.hasConnected = true;
387
388			if ( hasConnectionError() ) {
389				settings.errorcount = 0;
390				settings.connectionError = false;
391				$document.trigger( 'heartbeat-connection-restored' );
392				wp.hooks.doAction( 'heartbeat.connection-restored' );
393			}
394		}
395
396		/**
397		 * Gathers the data and connects to the server.
398		 *
399		 * @since 3.6.0
400		 * @access private
401		 *
402		 * @return {void}
403		 */
404		function connect() {
405			var ajaxData, heartbeatData;
406
407			// If the connection to the server is slower than the interval,
408			// heartbeat connects as soon as the previous connection's response is received.
409			if ( settings.connecting || settings.suspend ) {
410				return;
411			}
412
413			settings.lastTick = time();
414
415			heartbeatData = $.extend( {}, settings.queue );
416			// Clear the data queue. Anything added after this point will be sent on the next tick.
417			settings.queue = {};
418
419			$document.trigger( 'heartbeat-send', [ heartbeatData ] );
420			wp.hooks.doAction( 'heartbeat.send', heartbeatData );
421
422			ajaxData = {
423				data: heartbeatData,
424				interval: settings.tempInterval ? settings.tempInterval / 1000 : settings.mainInterval / 1000,
425				_nonce: typeof window.heartbeatSettings === 'object' ? window.heartbeatSettings.nonce : '',
426				action: 'heartbeat',
427				screen_id: settings.screenId,
428				has_focus: settings.hasFocus
429			};
430
431			if ( 'customize' === settings.screenId  ) {
432				ajaxData.wp_customize = 'on';
433			}
434
435			settings.connecting = true;
436			settings.xhr = $.ajax({
437				url: settings.url,
438				type: 'post',
439				timeout: 30000, // Throw an error if not completed after 30 seconds.
440				data: ajaxData,
441				dataType: 'json'
442			}).always( function() {
443				settings.connecting = false;
444				scheduleNextTick();
445			}).done( function( response, textStatus, jqXHR ) {
446				var newInterval;
447
448				if ( ! response ) {
449					setErrorState( 'empty' );
450					return;
451				}
452
453				clearErrorState();
454
455				if ( response.nonces_expired ) {
456					$document.trigger( 'heartbeat-nonces-expired' );
457					wp.hooks.doAction( 'heartbeat.nonces-expired' );
458				}
459
460				// Change the interval from PHP.
461				if ( response.heartbeat_interval ) {
462					newInterval = response.heartbeat_interval;
463					delete response.heartbeat_interval;
464				}
465
466				// Update the heartbeat nonce if set.
467				if ( response.heartbeat_nonce && typeof window.heartbeatSettings === 'object' ) {
468					window.heartbeatSettings.nonce = response.heartbeat_nonce;
469					delete response.heartbeat_nonce;
470				}
471
472				// Update the Rest API nonce if set and wp-api loaded.
473				if ( response.rest_nonce && typeof window.wpApiSettings === 'object' ) {
474					window.wpApiSettings.nonce = response.rest_nonce;
475					// This nonce is required for api-fetch through heartbeat.tick.
476					// delete response.rest_nonce;
477				}
478
479				$document.trigger( 'heartbeat-tick', [response, textStatus, jqXHR] );
480				wp.hooks.doAction( 'heartbeat.tick', response, textStatus, jqXHR );
481
482				// Do this last. Can trigger the next XHR if connection time > 5 seconds and newInterval == 'fast'.
483				if ( newInterval ) {
484					interval( newInterval );
485				}
486			}).fail( function( jqXHR, textStatus, error ) {
487				setErrorState( textStatus || 'unknown', jqXHR.status );
488				$document.trigger( 'heartbeat-error', [jqXHR, textStatus, error] );
489				wp.hooks.doAction( 'heartbeat.error', jqXHR, textStatus, error );
490			});
491		}
492
493		/**
494		 * Schedules the next connection.
495		 *
496		 * Fires immediately if the connection time is longer than the interval.
497		 *
498		 * @since 3.8.0
499		 * @access private
500		 *
501		 * @return {void}
502		 */
503		function scheduleNextTick() {
504			var delta = time() - settings.lastTick,
505				interval = settings.mainInterval;
506
507			if ( settings.suspend ) {
508				return;
509			}
510
511			if ( ! settings.hasFocus ) {
512				interval = 120000; // 120 seconds. Post locks expire after 150 seconds.
513			} else if ( settings.countdown > 0 && settings.tempInterval ) {
514				interval = settings.tempInterval;
515				settings.countdown--;
516
517				if ( settings.countdown < 1 ) {
518					settings.tempInterval = 0;
519				}
520			}
521
522			if ( settings.minimalInterval && interval < settings.minimalInterval ) {
523				interval = settings.minimalInterval;
524			}
525
526			window.clearTimeout( settings.beatTimer );
527
528			if ( delta < interval ) {
529				settings.beatTimer = window.setTimeout(
530					function() {
531						connect();
532					},
533					interval - delta
534				);
535			} else {
536				connect();
537			}
538		}
539
540		/**
541		 * Sets the internal state when the browser window becomes hidden or loses focus.
542		 *
543		 * @since 3.6.0
544		 * @access private
545		 *
546		 * @return {void}
547		 */
548		function blurred() {
549			settings.hasFocus = false;
550		}
551
552		/**
553		 * Sets the internal state when the browser window becomes visible or is in focus.
554		 *
555		 * @since 3.6.0
556		 * @access private
557		 *
558		 * @return {void}
559		 */
560		function focused() {
561			settings.userActivity = time();
562
563			// Resume if suspended.
564			resume();
565
566			if ( ! settings.hasFocus ) {
567				settings.hasFocus = true;
568				scheduleNextTick();
569			}
570		}
571
572		/**
573		 * Suspends connecting.
574		 */
575		function suspend() {
576			settings.suspend = true;
577		}
578
579		/**
580		 * Resumes connecting.
581		 */
582		function resume() {
583			settings.suspend = false;
584		}
585
586		/**
587		 * Runs when the user becomes active after a period of inactivity.
588		 *
589		 * @since 3.6.0
590		 * @access private
591		 *
592		 * @return {void}
593		 */
594		function userIsActive() {
595			settings.userActivityEvents = false;
596			$document.off( '.wp-heartbeat-active' );
597
598			$('iframe').each( function( i, frame ) {
599				if ( isLocalFrame( frame ) ) {
600					$( frame.contentWindow ).off( '.wp-heartbeat-active' );
601				}
602			});
603
604			focused();
605		}
606
607		/**
608		 * Checks for user activity.
609		 *
610		 * Runs every 30 seconds. Sets 'hasFocus = true' if user is active and the window
611		 * is in the background. Sets 'hasFocus = false' if the user has been inactive
612		 * (no mouse or keyboard activity) for 5 minutes even when the window has focus.
613		 *
614		 * @since 3.8.0
615		 * @access private
616		 *
617		 * @return {void}
618		 */
619		function checkUserActivity() {
620			var lastActive = settings.userActivity ? time() - settings.userActivity : 0;
621
622			// Throttle down when no mouse or keyboard activity for 5 minutes.
623			if ( lastActive > 300000 && settings.hasFocus ) {
624				blurred();
625			}
626
627			// Suspend after 10 minutes of inactivity when suspending is enabled.
628			// Always suspend after 60 minutes of inactivity. This will release the post lock, etc.
629			if ( ( settings.suspendEnabled && lastActive > 600000 ) || lastActive > 3600000 ) {
630				suspend();
631			}
632
633			if ( ! settings.userActivityEvents ) {
634				$document.on( 'mouseover.wp-heartbeat-active keyup.wp-heartbeat-active touchend.wp-heartbeat-active', function() {
635					userIsActive();
636				});
637
638				$('iframe').each( function( i, frame ) {
639					if ( isLocalFrame( frame ) ) {
640						$( frame.contentWindow ).on( 'mouseover.wp-heartbeat-active keyup.wp-heartbeat-active touchend.wp-heartbeat-active', function() {
641							userIsActive();
642						});
643					}
644				});
645
646				settings.userActivityEvents = true;
647			}
648		}
649
650		// Public methods.
651
652		/**
653		 * Checks whether the window (or any local iframe in it) has focus, or the user
654		 * is active.
655		 *
656		 * @since 3.6.0
657		 * @memberOf wp.heartbeat.prototype
658		 *
659		 * @return {boolean} True if the window or the user is active.
660		 */
661		function hasFocus() {
662			return settings.hasFocus;
663		}
664
665		/**
666		 * Checks whether there is a connection error.
667		 *
668		 * @since 3.6.0
669		 *
670		 * @memberOf wp.heartbeat.prototype
671		 *
672		 * @return {boolean} True if a connection error was found.
673		 */
674		function hasConnectionError() {
675			return settings.connectionError;
676		}
677
678		/**
679		 * Connects as soon as possible regardless of 'hasFocus' state.
680		 *
681		 * Will not open two concurrent connections. If a connection is in progress,
682		 * will connect again immediately after the current connection completes.
683		 *
684		 * @since 3.8.0
685		 *
686		 * @memberOf wp.heartbeat.prototype
687		 *
688		 * @return {void}
689		 */
690		function connectNow() {
691			settings.lastTick = 0;
692			scheduleNextTick();
693		}
694
695		/**
696		 * Disables suspending.
697		 *
698		 * Should be used only when Heartbeat is performing critical tasks like
699		 * autosave, post-locking, etc. Using this on many screens may overload
700		 * the user's hosting account if several browser windows/tabs are left open
701		 * for a long time.
702		 *
703		 * @since 3.8.0
704		 *
705		 * @memberOf wp.heartbeat.prototype
706		 *
707		 * @return {void}
708		 */
709		function disableSuspend() {
710			settings.suspendEnabled = false;
711		}
712
713		/**
714		 * Gets/Sets the interval.
715		 *
716		 * When setting to 'fast' or 5, the interval is 5 seconds for the next 30 ticks
717		 * (for 2 minutes and 30 seconds) by default. In this case the number of 'ticks'
718		 * can be passed as second argument. If the window doesn't have focus,
719		 * the interval slows down to 2 minutes.
720		 *
721		 * @since 3.6.0
722		 *
723		 * @memberOf wp.heartbeat.prototype
724		 *
725		 * @param {string|number} speed Interval: 'fast' or integer between 1 and 3600 (seconds).
726		 *                              Fast equals 5.
727		 * @param {number}        ticks Tells how many ticks before the interval reverts back.
728		 *                              Value must be between 1 and 30. Used with speed = 'fast' or 5.
729		 *
730		 * @return {number} Current interval in seconds.
731		 */
732		function interval( speed, ticks ) {
733			var newInterval,
734				oldInterval = settings.tempInterval ? settings.tempInterval : settings.mainInterval;
735
736			if ( speed ) {
737				if ( 'fast' === speed ) {
738					// Special case, see below.
739					newInterval = 5000;
740				} else if ( 'long-polling' === speed ) {
741					// Allow long polling (experimental).
742					settings.mainInterval = 0;
743					return 0;
744				} else {
745					speed = parseInt( speed, 10 );
746
747					if ( speed >= 1 && speed <= 3600 ) {
748						newInterval = speed * 1000;
749					} else {
750						newInterval = settings.originalInterval;
751					}
752				}
753
754				if ( settings.minimalInterval && newInterval < settings.minimalInterval ) {
755					newInterval = settings.minimalInterval;
756				}
757
758				// Special case, runs for a number of ticks then reverts to the previous interval.
759				if ( 5000 === newInterval ) {
760					ticks = parseInt( ticks, 10 ) || 30;
761					ticks = ticks < 1 || ticks > 30 ? 30 : ticks;
762
763					settings.countdown = ticks;
764					settings.tempInterval = newInterval;
765				} else {
766					settings.countdown = 0;
767					settings.tempInterval = 0;
768					settings.mainInterval = newInterval;
769				}
770
771				/*
772				 * Change the next connection time if new interval has been set.
773				 * Will connect immediately if the time since the last connection
774				 * is greater than the new interval.
775				 */
776				if ( newInterval !== oldInterval ) {
777					scheduleNextTick();
778				}
779			}
780
781			return settings.tempInterval ? settings.tempInterval / 1000 : settings.mainInterval / 1000;
782		}
783
784		/**
785		 * Enqueues data to send with the next XHR.
786		 *
787		 * As the data is send asynchronously, this function doesn't return the XHR
788		 * response. To see the response, use the custom jQuery event 'heartbeat-tick'
789		 * on the document, example:
790		 *		$(document).on( 'heartbeat-tick.myname', function( event, data, textStatus, jqXHR ) {
791		 *			// code
792		 *		});
793		 * If the same 'handle' is used more than once, the data is not overwritten when
794		 * the third argument is 'true'. Use `wp.heartbeat.isQueued('handle')` to see if
795		 * any data is already queued for that handle.
796		 *
797		 * @since 3.6.0
798		 *
799		 * @memberOf wp.heartbeat.prototype
800		 *
801		 * @param {string}  handle      Unique handle for the data, used in PHP to
802		 *                              receive the data.
803		 * @param {*}       data        The data to send.
804		 * @param {boolean} noOverwrite Whether to overwrite existing data in the queue.
805		 *
806		 * @return {boolean} True if the data was queued.
807		 */
808		function enqueue( handle, data, noOverwrite ) {
809			if ( handle ) {
810				if ( noOverwrite && this.isQueued( handle ) ) {
811					return false;
812				}
813
814				settings.queue[handle] = data;
815				return true;
816			}
817			return false;
818		}
819
820		/**
821		 * Checks if data with a particular handle is queued.
822		 *
823		 * @since 3.6.0
824		 *
825		 * @param {string} handle The handle for the data.
826		 *
827		 * @return {boolean} True if the data is queued with this handle.
828		 */
829		function isQueued( handle ) {
830			if ( handle ) {
831				return settings.queue.hasOwnProperty( handle );
832			}
833		}
834
835		/**
836		 * Removes data with a particular handle from the queue.
837		 *
838		 * @since 3.7.0
839		 *
840		 * @memberOf wp.heartbeat.prototype
841		 *
842		 * @param {string} handle The handle for the data.
843		 *
844		 * @return {void}
845		 */
846		function dequeue( handle ) {
847			if ( handle ) {
848				delete settings.queue[handle];
849			}
850		}
851
852		/**
853		 * Gets data that was enqueued with a particular handle.
854		 *
855		 * @since 3.7.0
856		 *
857		 * @memberOf wp.heartbeat.prototype
858		 *
859		 * @param {string} handle The handle for the data.
860		 *
861		 * @return {*} The data or undefined.
862		 */
863		function getQueuedItem( handle ) {
864			if ( handle ) {
865				return this.isQueued( handle ) ? settings.queue[handle] : undefined;
866			}
867		}
868
869		initialize();
870
871		// Expose public methods.
872		return {
873			hasFocus: hasFocus,
874			connectNow: connectNow,
875			disableSuspend: disableSuspend,
876			interval: interval,
877			hasConnectionError: hasConnectionError,
878			enqueue: enqueue,
879			dequeue: dequeue,
880			isQueued: isQueued,
881			getQueuedItem: getQueuedItem
882		};
883	};
884
885	/**
886	 * Ensure the global `wp` object exists.
887	 *
888	 * @namespace wp
889	 */
890	window.wp = window.wp || {};
891
892	/**
893	 * Contains the Heartbeat API.
894	 *
895	 * @namespace wp.heartbeat
896	 * @type {Heartbeat}
897	 */
898	window.wp.heartbeat = new Heartbeat();
899
900}( jQuery, window ));
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