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   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                   * The interval can be from 15 to 120 seconds and can be set temporarily to 5 seconds.
 136                   * It can be set in the initial options or changed later through JS and/or through PHP.
 137                   */
 138                  if ( options.interval ) {
 139                      settings.mainInterval = options.interval;
 140  
 141                      if ( settings.mainInterval < 15 ) {
 142                          settings.mainInterval = 15;
 143                      } else if ( settings.mainInterval > 120 ) {
 144                          settings.mainInterval = 120;
 145                      }
 146                  }
 147  
 148                  /*
 149                   * Used to limit the number of AJAX requests. Overrides all other intervals
 150                   * if they are shorter. Needed for some hosts that cannot handle frequent requests
 151                   * and the user may exceed the allocated server CPU time, etc. The minimal interval
 152                   * can be up to 600 seconds, however setting it to longer than 120 seconds
 153                   * will limit or disable some of the functionality (like post locks).
 154                   * Once set at initialization, minimalInterval cannot be changed/overridden.
 155                   */
 156                  if ( options.minimalInterval ) {
 157                      options.minimalInterval = parseInt( options.minimalInterval, 10 );
 158                      settings.minimalInterval = options.minimalInterval > 0 && options.minimalInterval <= 600 ? options.minimalInterval * 1000 : 0;
 159                  }
 160  
 161                  if ( settings.minimalInterval && settings.mainInterval < settings.minimalInterval ) {
 162                      settings.mainInterval = settings.minimalInterval;
 163                  }
 164  
 165                  // 'screenId' can be added from settings on the front end where the JS global
 166                  // 'pagenow' is not set.
 167                  if ( ! settings.screenId ) {
 168                      settings.screenId = options.screenId || 'front';
 169                  }
 170  
 171                  if ( options.suspension === 'disable' ) {
 172                      settings.suspendEnabled = false;
 173                  }
 174              }
 175  
 176              // Convert to milliseconds.
 177              settings.mainInterval = settings.mainInterval * 1000;
 178              settings.originalInterval = settings.mainInterval;
 179  
 180              /*
 181               * Switch the interval to 120 seconds by using the Page Visibility API.
 182               * If the browser doesn't support it (Safari < 7, Android < 4.4, IE < 10), the
 183               * interval will be increased to 120 seconds after 5 minutes of mouse and keyboard
 184               * inactivity.
 185               */
 186              if ( typeof document.hidden !== 'undefined' ) {
 187                  hidden = 'hidden';
 188                  visibilitychange = 'visibilitychange';
 189                  visibilityState = 'visibilityState';
 190              } else if ( typeof document.msHidden !== 'undefined' ) { // IE10.
 191                  hidden = 'msHidden';
 192                  visibilitychange = 'msvisibilitychange';
 193                  visibilityState = 'msVisibilityState';
 194              } else if ( typeof document.webkitHidden !== 'undefined' ) { // Android.
 195                  hidden = 'webkitHidden';
 196                  visibilitychange = 'webkitvisibilitychange';
 197                  visibilityState = 'webkitVisibilityState';
 198              }
 199  
 200              if ( hidden ) {
 201                  if ( document[hidden] ) {
 202                      settings.hasFocus = false;
 203                  }
 204  
 205                  $document.on( visibilitychange + '.wp-heartbeat', function() {
 206                      if ( document[visibilityState] === 'hidden' ) {
 207                          blurred();
 208                          window.clearInterval( settings.checkFocusTimer );
 209                      } else {
 210                          focused();
 211                          if ( document.hasFocus ) {
 212                              settings.checkFocusTimer = window.setInterval( checkFocus, 10000 );
 213                          }
 214                      }
 215                  });
 216              }
 217  
 218              // Use document.hasFocus() if available.
 219              if ( document.hasFocus ) {
 220                  settings.checkFocusTimer = window.setInterval( checkFocus, 10000 );
 221              }
 222  
 223              $(window).on( 'unload.wp-heartbeat', function() {
 224                  // Don't connect anymore.
 225                  settings.suspend = true;
 226  
 227                  // Abort the last request if not completed.
 228                  if ( settings.xhr && settings.xhr.readyState !== 4 ) {
 229                      settings.xhr.abort();
 230                  }
 231              });
 232  
 233              // Check for user activity every 30 seconds.
 234              window.setInterval( checkUserActivity, 30000 );
 235  
 236              // Start one tick after DOM ready.
 237              $document.ready( function() {
 238                  settings.lastTick = time();
 239                  scheduleNextTick();
 240              });
 241          }
 242  
 243          /**
 244           * Returns the current time according to the browser.
 245           *
 246           * @since 3.6.0
 247           * @access private
 248           *
 249           * @return {number} Returns the current time.
 250           */
 251  		function time() {
 252              return (new Date()).getTime();
 253          }
 254  
 255          /**
 256           * Checks if the iframe is from the same origin.
 257           *
 258           * @since 3.6.0
 259           * @access private
 260           *
 261           * @return {boolean} Returns whether or not the iframe is from the same origin.
 262           */
 263  		function isLocalFrame( frame ) {
 264              var origin, src = frame.src;
 265  
 266              /*
 267               * Need to compare strings as WebKit doesn't throw JS errors when iframes have
 268               * different origin. It throws uncatchable exceptions.
 269               */
 270              if ( src && /^https?:\/\//.test( src ) ) {
 271                  origin = window.location.origin ? window.location.origin : window.location.protocol + '//' + window.location.host;
 272  
 273                  if ( src.indexOf( origin ) !== 0 ) {
 274                      return false;
 275                  }
 276              }
 277  
 278              try {
 279                  if ( frame.contentWindow.document ) {
 280                      return true;
 281                  }
 282              } catch(e) {}
 283  
 284              return false;
 285          }
 286  
 287          /**
 288           * Checks if the document's focus has changed.
 289           *
 290           * @since 4.1.0
 291           * @access private
 292           *
 293           * @return {void}
 294           */
 295  		function checkFocus() {
 296              if ( settings.hasFocus && ! document.hasFocus() ) {
 297                  blurred();
 298              } else if ( ! settings.hasFocus && document.hasFocus() ) {
 299                  focused();
 300              }
 301          }
 302  
 303          /**
 304           * Sets error state and fires an event on XHR errors or timeout.
 305           *
 306           * @since 3.8.0
 307           * @access private
 308           *
 309           * @param {string} error  The error type passed from the XHR.
 310           * @param {number} status The HTTP status code passed from jqXHR
 311           *                        (200, 404, 500, etc.).
 312           *
 313           * @return {void}
 314           */
 315  		function setErrorState( error, status ) {
 316              var trigger;
 317  
 318              if ( error ) {
 319                  switch ( error ) {
 320                      case 'abort':
 321                          // Do nothing.
 322                          break;
 323                      case 'timeout':
 324                          // No response for 30 seconds.
 325                          trigger = true;
 326                          break;
 327                      case 'error':
 328                          if ( 503 === status && settings.hasConnected ) {
 329                              trigger = true;
 330                              break;
 331                          }
 332                          /* falls through */
 333                      case 'parsererror':
 334                      case 'empty':
 335                      case 'unknown':
 336                          settings.errorcount++;
 337  
 338                          if ( settings.errorcount > 2 && settings.hasConnected ) {
 339                              trigger = true;
 340                          }
 341  
 342                          break;
 343                  }
 344  
 345                  if ( trigger && ! hasConnectionError() ) {
 346                      settings.connectionError = true;
 347                      $document.trigger( 'heartbeat-connection-lost', [error, status] );
 348                      wp.hooks.doAction( 'heartbeat.connection-lost', error, status );
 349                  }
 350              }
 351          }
 352  
 353          /**
 354           * Clears the error state and fires an event if there is a connection error.
 355           *
 356           * @since 3.8.0
 357           * @access private
 358           *
 359           * @return {void}
 360           */
 361  		function clearErrorState() {
 362              // Has connected successfully.
 363              settings.hasConnected = true;
 364  
 365              if ( hasConnectionError() ) {
 366                  settings.errorcount = 0;
 367                  settings.connectionError = false;
 368                  $document.trigger( 'heartbeat-connection-restored' );
 369                  wp.hooks.doAction( 'heartbeat.connection-restored' );
 370              }
 371          }
 372  
 373          /**
 374           * Gathers the data and connects to the server.
 375           *
 376           * @since 3.6.0
 377           * @access private
 378           *
 379           * @return {void}
 380           */
 381  		function connect() {
 382              var ajaxData, heartbeatData;
 383  
 384              // If the connection to the server is slower than the interval,
 385              // heartbeat connects as soon as the previous connection's response is received.
 386              if ( settings.connecting || settings.suspend ) {
 387                  return;
 388              }
 389  
 390              settings.lastTick = time();
 391  
 392              heartbeatData = $.extend( {}, settings.queue );
 393              // Clear the data queue. Anything added after this point will be sent on the next tick.
 394              settings.queue = {};
 395  
 396              $document.trigger( 'heartbeat-send', [ heartbeatData ] );
 397              wp.hooks.doAction( 'heartbeat.send', heartbeatData );
 398  
 399              ajaxData = {
 400                  data: heartbeatData,
 401                  interval: settings.tempInterval ? settings.tempInterval / 1000 : settings.mainInterval / 1000,
 402                  _nonce: typeof window.heartbeatSettings === 'object' ? window.heartbeatSettings.nonce : '',
 403                  action: 'heartbeat',
 404                  screen_id: settings.screenId,
 405                  has_focus: settings.hasFocus
 406              };
 407  
 408              if ( 'customize' === settings.screenId  ) {
 409                  ajaxData.wp_customize = 'on';
 410              }
 411  
 412              settings.connecting = true;
 413              settings.xhr = $.ajax({
 414                  url: settings.url,
 415                  type: 'post',
 416                  timeout: 30000, // Throw an error if not completed after 30 seconds.
 417                  data: ajaxData,
 418                  dataType: 'json'
 419              }).always( function() {
 420                  settings.connecting = false;
 421                  scheduleNextTick();
 422              }).done( function( response, textStatus, jqXHR ) {
 423                  var newInterval;
 424  
 425                  if ( ! response ) {
 426                      setErrorState( 'empty' );
 427                      return;
 428                  }
 429  
 430                  clearErrorState();
 431  
 432                  if ( response.nonces_expired ) {
 433                      $document.trigger( 'heartbeat-nonces-expired' );
 434                      wp.hooks.doAction( 'heartbeat.nonces-expired' );
 435                  }
 436  
 437                  // Change the interval from PHP.
 438                  if ( response.heartbeat_interval ) {
 439                      newInterval = response.heartbeat_interval;
 440                      delete response.heartbeat_interval;
 441                  }
 442  
 443                  // Update the heartbeat nonce if set.
 444                  if ( response.heartbeat_nonce && typeof window.heartbeatSettings === 'object' ) {
 445                      window.heartbeatSettings.nonce = response.heartbeat_nonce;
 446                      delete response.heartbeat_nonce;
 447                  }
 448  
 449                  // Update the Rest API nonce if set and wp-api loaded.
 450                  if ( response.rest_nonce && typeof window.wpApiSettings === 'object' ) {
 451                      window.wpApiSettings.nonce = response.rest_nonce;
 452                      // This nonce is required for api-fetch through heartbeat.tick.
 453                      // delete response.rest_nonce;
 454                  }
 455  
 456                  $document.trigger( 'heartbeat-tick', [response, textStatus, jqXHR] );
 457                  wp.hooks.doAction( 'heartbeat.tick', response, textStatus, jqXHR );
 458  
 459                  // Do this last. Can trigger the next XHR if connection time > 5 seconds and newInterval == 'fast'.
 460                  if ( newInterval ) {
 461                      interval( newInterval );
 462                  }
 463              }).fail( function( jqXHR, textStatus, error ) {
 464                  setErrorState( textStatus || 'unknown', jqXHR.status );
 465                  $document.trigger( 'heartbeat-error', [jqXHR, textStatus, error] );
 466                  wp.hooks.doAction( 'heartbeat.error', jqXHR, textStatus, error );
 467              });
 468          }
 469  
 470          /**
 471           * Schedules the next connection.
 472           *
 473           * Fires immediately if the connection time is longer than the interval.
 474           *
 475           * @since 3.8.0
 476           * @access private
 477           *
 478           * @return {void}
 479           */
 480  		function scheduleNextTick() {
 481              var delta = time() - settings.lastTick,
 482                  interval = settings.mainInterval;
 483  
 484              if ( settings.suspend ) {
 485                  return;
 486              }
 487  
 488              if ( ! settings.hasFocus ) {
 489                  interval = 120000; // 120 seconds. Post locks expire after 150 seconds.
 490              } else if ( settings.countdown > 0 && settings.tempInterval ) {
 491                  interval = settings.tempInterval;
 492                  settings.countdown--;
 493  
 494                  if ( settings.countdown < 1 ) {
 495                      settings.tempInterval = 0;
 496                  }
 497              }
 498  
 499              if ( settings.minimalInterval && interval < settings.minimalInterval ) {
 500                  interval = settings.minimalInterval;
 501              }
 502  
 503              window.clearTimeout( settings.beatTimer );
 504  
 505              if ( delta < interval ) {
 506                  settings.beatTimer = window.setTimeout(
 507                      function() {
 508                          connect();
 509                      },
 510                      interval - delta
 511                  );
 512              } else {
 513                  connect();
 514              }
 515          }
 516  
 517          /**
 518           * Sets the internal state when the browser window becomes hidden or loses focus.
 519           *
 520           * @since 3.6.0
 521           * @access private
 522           *
 523           * @return {void}
 524           */
 525  		function blurred() {
 526              settings.hasFocus = false;
 527          }
 528  
 529          /**
 530           * Sets the internal state when the browser window becomes visible or is in focus.
 531           *
 532           * @since 3.6.0
 533           * @access private
 534           *
 535           * @return {void}
 536           */
 537  		function focused() {
 538              settings.userActivity = time();
 539  
 540              // Resume if suspended.
 541              settings.suspend = false;
 542  
 543              if ( ! settings.hasFocus ) {
 544                  settings.hasFocus = true;
 545                  scheduleNextTick();
 546              }
 547          }
 548  
 549          /**
 550           * Runs when the user becomes active after a period of inactivity.
 551           *
 552           * @since 3.6.0
 553           * @access private
 554           *
 555           * @return {void}
 556           */
 557  		function userIsActive() {
 558              settings.userActivityEvents = false;
 559              $document.off( '.wp-heartbeat-active' );
 560  
 561              $('iframe').each( function( i, frame ) {
 562                  if ( isLocalFrame( frame ) ) {
 563                      $( frame.contentWindow ).off( '.wp-heartbeat-active' );
 564                  }
 565              });
 566  
 567              focused();
 568          }
 569  
 570          /**
 571           * Checks for user activity.
 572           *
 573           * Runs every 30 seconds. Sets 'hasFocus = true' if user is active and the window
 574           * is in the background. Sets 'hasFocus = false' if the user has been inactive
 575           * (no mouse or keyboard activity) for 5 minutes even when the window has focus.
 576           *
 577           * @since 3.8.0
 578           * @access private
 579           *
 580           * @return {void}
 581           */
 582  		function checkUserActivity() {
 583              var lastActive = settings.userActivity ? time() - settings.userActivity : 0;
 584  
 585              // Throttle down when no mouse or keyboard activity for 5 minutes.
 586              if ( lastActive > 300000 && settings.hasFocus ) {
 587                  blurred();
 588              }
 589  
 590              // Suspend after 10 minutes of inactivity when suspending is enabled.
 591              // Always suspend after 60 minutes of inactivity. This will release the post lock, etc.
 592              if ( ( settings.suspendEnabled && lastActive > 600000 ) || lastActive > 3600000 ) {
 593                  settings.suspend = true;
 594              }
 595  
 596              if ( ! settings.userActivityEvents ) {
 597                  $document.on( 'mouseover.wp-heartbeat-active keyup.wp-heartbeat-active touchend.wp-heartbeat-active', function() {
 598                      userIsActive();
 599                  });
 600  
 601                  $('iframe').each( function( i, frame ) {
 602                      if ( isLocalFrame( frame ) ) {
 603                          $( frame.contentWindow ).on( 'mouseover.wp-heartbeat-active keyup.wp-heartbeat-active touchend.wp-heartbeat-active', function() {
 604                              userIsActive();
 605                          });
 606                      }
 607                  });
 608  
 609                  settings.userActivityEvents = true;
 610              }
 611          }
 612  
 613          // Public methods.
 614  
 615          /**
 616           * Checks whether the window (or any local iframe in it) has focus, or the user
 617           * is active.
 618           *
 619           * @since 3.6.0
 620           * @memberOf wp.heartbeat.prototype
 621           *
 622           * @return {boolean} True if the window or the user is active.
 623           */
 624  		function hasFocus() {
 625              return settings.hasFocus;
 626          }
 627  
 628          /**
 629           * Checks whether there is a connection error.
 630           *
 631           * @since 3.6.0
 632           *
 633           * @memberOf wp.heartbeat.prototype
 634           *
 635           * @return {boolean} True if a connection error was found.
 636           */
 637  		function hasConnectionError() {
 638              return settings.connectionError;
 639          }
 640  
 641          /**
 642           * Connects as soon as possible regardless of 'hasFocus' state.
 643           *
 644           * Will not open two concurrent connections. If a connection is in progress,
 645           * will connect again immediately after the current connection completes.
 646           *
 647           * @since 3.8.0
 648           *
 649           * @memberOf wp.heartbeat.prototype
 650           *
 651           * @return {void}
 652           */
 653  		function connectNow() {
 654              settings.lastTick = 0;
 655              scheduleNextTick();
 656          }
 657  
 658          /**
 659           * Disables suspending.
 660           *
 661           * Should be used only when Heartbeat is performing critical tasks like
 662           * autosave, post-locking, etc. Using this on many screens may overload
 663           * the user's hosting account if several browser windows/tabs are left open
 664           * for a long time.
 665           *
 666           * @since 3.8.0
 667           *
 668           * @memberOf wp.heartbeat.prototype
 669           *
 670           * @return {void}
 671           */
 672  		function disableSuspend() {
 673              settings.suspendEnabled = false;
 674          }
 675  
 676          /**
 677           * Gets/Sets the interval.
 678           *
 679           * When setting to 'fast' or 5, the interval is 5 seconds for the next 30 ticks
 680           * (for 2 minutes and 30 seconds) by default. In this case the number of 'ticks'
 681           * can be passed as second argument. If the window doesn't have focus,
 682           * the interval slows down to 2 minutes.
 683           *
 684           * @since 3.6.0
 685           *
 686           * @memberOf wp.heartbeat.prototype
 687           *
 688           * @param {string|number} speed Interval: 'fast' or 5, 15, 30, 60, 120.
 689           *                              Fast equals 5.
 690           * @param {string}        ticks Tells how many ticks before the interval reverts
 691           *                              back. Used with speed = 'fast' or 5.
 692           *
 693           * @return {number} Current interval in seconds.
 694           */
 695  		function interval( speed, ticks ) {
 696              var newInterval,
 697                  oldInterval = settings.tempInterval ? settings.tempInterval : settings.mainInterval;
 698  
 699              if ( speed ) {
 700                  switch ( speed ) {
 701                      case 'fast':
 702                      case 5:
 703                          newInterval = 5000;
 704                          break;
 705                      case 15:
 706                          newInterval = 15000;
 707                          break;
 708                      case 30:
 709                          newInterval = 30000;
 710                          break;
 711                      case 60:
 712                          newInterval = 60000;
 713                          break;
 714                      case 120:
 715                          newInterval = 120000;
 716                          break;
 717                      case 'long-polling':
 718                          // Allow long polling (experimental).
 719                          settings.mainInterval = 0;
 720                          return 0;
 721                      default:
 722                          newInterval = settings.originalInterval;
 723                  }
 724  
 725                  if ( settings.minimalInterval && newInterval < settings.minimalInterval ) {
 726                      newInterval = settings.minimalInterval;
 727                  }
 728  
 729                  if ( 5000 === newInterval ) {
 730                      ticks = parseInt( ticks, 10 ) || 30;
 731                      ticks = ticks < 1 || ticks > 30 ? 30 : ticks;
 732  
 733                      settings.countdown = ticks;
 734                      settings.tempInterval = newInterval;
 735                  } else {
 736                      settings.countdown = 0;
 737                      settings.tempInterval = 0;
 738                      settings.mainInterval = newInterval;
 739                  }
 740  
 741                  /*
 742                   * Change the next connection time if new interval has been set.
 743                   * Will connect immediately if the time since the last connection
 744                   * is greater than the new interval.
 745                   */
 746                  if ( newInterval !== oldInterval ) {
 747                      scheduleNextTick();
 748                  }
 749              }
 750  
 751              return settings.tempInterval ? settings.tempInterval / 1000 : settings.mainInterval / 1000;
 752          }
 753  
 754          /**
 755           * Enqueues data to send with the next XHR.
 756           *
 757           * As the data is send asynchronously, this function doesn't return the XHR
 758           * response. To see the response, use the custom jQuery event 'heartbeat-tick'
 759           * on the document, example:
 760           *        $(document).on( 'heartbeat-tick.myname', function( event, data, textStatus, jqXHR ) {
 761           *            // code
 762           *        });
 763           * If the same 'handle' is used more than once, the data is not overwritten when
 764           * the third argument is 'true'. Use `wp.heartbeat.isQueued('handle')` to see if
 765           * any data is already queued for that handle.
 766           *
 767           * @since 3.6.0
 768           *
 769           * @memberOf wp.heartbeat.prototype
 770           *
 771           * @param {string}  handle      Unique handle for the data, used in PHP to
 772           *                              receive the data.
 773           * @param {*}       data        The data to send.
 774           * @param {boolean} noOverwrite Whether to overwrite existing data in the queue.
 775           *
 776           * @return {boolean} True if the data was queued.
 777           */
 778  		function enqueue( handle, data, noOverwrite ) {
 779              if ( handle ) {
 780                  if ( noOverwrite && this.isQueued( handle ) ) {
 781                      return false;
 782                  }
 783  
 784                  settings.queue[handle] = data;
 785                  return true;
 786              }
 787              return false;
 788          }
 789  
 790          /**
 791           * Checks if data with a particular handle is queued.
 792           *
 793           * @since 3.6.0
 794           *
 795           * @param {string} handle The handle for the data.
 796           *
 797           * @return {boolean} True if the data is queued with this handle.
 798           */
 799  		function isQueued( handle ) {
 800              if ( handle ) {
 801                  return settings.queue.hasOwnProperty( handle );
 802              }
 803          }
 804  
 805          /**
 806           * Removes data with a particular handle from the queue.
 807           *
 808           * @since 3.7.0
 809           *
 810           * @memberOf wp.heartbeat.prototype
 811           *
 812           * @param {string} handle The handle for the data.
 813           *
 814           * @return {void}
 815           */
 816  		function dequeue( handle ) {
 817              if ( handle ) {
 818                  delete settings.queue[handle];
 819              }
 820          }
 821  
 822          /**
 823           * Gets data that was enqueued with a particular handle.
 824           *
 825           * @since 3.7.0
 826           *
 827           * @memberOf wp.heartbeat.prototype
 828           *
 829           * @param {string} handle The handle for the data.
 830           *
 831           * @return {*} The data or undefined.
 832           */
 833  		function getQueuedItem( handle ) {
 834              if ( handle ) {
 835                  return this.isQueued( handle ) ? settings.queue[handle] : undefined;
 836              }
 837          }
 838  
 839          initialize();
 840  
 841          // Expose public methods.
 842          return {
 843              hasFocus: hasFocus,
 844              connectNow: connectNow,
 845              disableSuspend: disableSuspend,
 846              interval: interval,
 847              hasConnectionError: hasConnectionError,
 848              enqueue: enqueue,
 849              dequeue: dequeue,
 850              isQueued: isQueued,
 851              getQueuedItem: getQueuedItem
 852          };
 853      };
 854  
 855      /**
 856       * Ensure the global `wp` object exists.
 857       *
 858       * @namespace wp
 859       */
 860      window.wp = window.wp || {};
 861  
 862      /**
 863       * Contains the Heartbeat API.
 864       *
 865       * @namespace wp.heartbeat
 866       * @type {Heartbeat}
 867       */
 868      window.wp.heartbeat = new Heartbeat();
 869  
 870  }( jQuery, window ));