Site Builder

Editing: customize-preview.js

writable 0666

/*
 * Script run inside a Customizer preview frame.
 *
 * @output wp-includes/js/customize-preview.js
 */
(function( exports, $ ){
	var api = wp.customize,
		debounce,
		currentHistoryState = {};

/*
	 * Capture the state that is passed into history.replaceState() and history.pushState()
	 * and also which is returned in the popstate event so that when the changeset_uuid
	 * gets updated when transitioning to a new changeset there the current state will
	 * be supplied in the call to history.replaceState().
	 */
	( function( history ) {
		var injectUrlWithState;

if ( ! history.replaceState ) {
			return;
		}

/**
		 * Amend the supplied URL with the customized state.
		 *
		 * @since 4.7.0
		 * @access private
		 *
		 * @param {string} url URL.
		 * @return {string} URL with customized state.
		 */
		injectUrlWithState = function( url ) {
			var urlParser, oldQueryParams, newQueryParams;
			urlParser = document.createElement( 'a' );
			urlParser.href = url;
			oldQueryParams = api.utils.parseQueryString( location.search.substr( 1 ) );
			newQueryParams = api.utils.parseQueryString( urlParser.search.substr( 1 ) );

newQueryParams.customize_changeset_uuid = oldQueryParams.customize_changeset_uuid;
			if ( oldQueryParams.customize_autosaved ) {
				newQueryParams.customize_autosaved = 'on';
			}
			if ( oldQueryParams.customize_theme ) {
				newQueryParams.customize_theme = oldQueryParams.customize_theme;
			}
			if ( oldQueryParams.customize_messenger_channel ) {
				newQueryParams.customize_messenger_channel = oldQueryParams.customize_messenger_channel;
			}
			urlParser.search = $.param( newQueryParams );
			return urlParser.href;
		};

history.replaceState = ( function( nativeReplaceState ) {
			return function historyReplaceState( data, title, url ) {
				currentHistoryState = data;
				return nativeReplaceState.call( history, data, title, 'string' === typeof url && url.length > 0 ? injectUrlWithState( url ) : url );
			};
		} )( history.replaceState );

history.pushState = ( function( nativePushState ) {
			return function historyPushState( data, title, url ) {
				currentHistoryState = data;
				return nativePushState.call( history, data, title, 'string' === typeof url && url.length > 0 ? injectUrlWithState( url ) : url );
			};
		} )( history.pushState );

window.addEventListener( 'popstate', function( event ) {
			currentHistoryState = event.state;
		} );

}( history ) );

/**
	 * Returns a debounced version of the function.
	 *
	 * @todo Require Underscore.js for this file and retire this.
	 */
	debounce = function( fn, delay, context ) {
		var timeout;
		return function() {
			var args = arguments;

context = context || this;

clearTimeout( timeout );
			timeout = setTimeout( function() {
				timeout = null;
				fn.apply( context, args );
			}, delay );
		};
	};

/**
	 * @memberOf wp.customize
	 * @alias wp.customize.Preview
	 *
	 * @constructor
	 * @augments wp.customize.Messenger
	 * @augments wp.customize.Class
	 * @mixes wp.customize.Events
	 */
	api.Preview = api.Messenger.extend(/** @lends wp.customize.Preview.prototype */{
		/**
		 * @param {Object} params  - Parameters to configure the messenger.
		 * @param {Object} options - Extend any instance parameter or method with this object.
		 */
		initialize: function( params, options ) {
			var preview = this, urlParser = document.createElement( 'a' );

api.Messenger.prototype.initialize.call( preview, params, options );

urlParser.href = preview.origin();
			preview.add( 'scheme', urlParser.protocol.replace( /:$/, '' ) );

preview.body = $( document.body );
			preview.window = $( window );

if ( api.settings.channel ) {

// If in an iframe, then intercept the link clicks and form submissions.
				preview.body.on( 'click.preview', 'a', function( event ) {
					preview.handleLinkClick( event );
				} );
				preview.body.on( 'submit.preview', 'form', function( event ) {
					preview.handleFormSubmit( event );
				} );

preview.window.on( 'scroll.preview', debounce( function() {
					preview.send( 'scroll', preview.window.scrollTop() );
				}, 200 ) );

preview.bind( 'scroll', function( distance ) {
					preview.window.scrollTop( distance );
				});
			}
		},

/**
		 * Handle link clicks in preview.
		 *
		 * @since 4.7.0
		 * @access public
		 *
		 * @param {jQuery.Event} event Event.
		 */
		handleLinkClick: function( event ) {
			var preview = this, link, isInternalJumpLink;
			link = $( event.target ).closest( 'a' );

// No-op if the anchor is not a link.
			if ( _.isUndefined( link.attr( 'href' ) ) ) {
				return;
			}

// Allow internal jump links and JS links to behave normally without preventing default.
			isInternalJumpLink = ( '#' === link.attr( 'href' ).substr( 0, 1 ) );
			if ( isInternalJumpLink || ! /^https?:$/.test( link.prop( 'protocol' ) ) ) {
				return;
			}

// If the link is not previewable, prevent the browser from navigating to it.
			if ( ! api.isLinkPreviewable( link[0] ) ) {
				wp.a11y.speak( api.settings.l10n.linkUnpreviewable );
				event.preventDefault();
				return;
			}

// Prevent initiating navigating from click and instead rely on sending url message to pane.
			event.preventDefault();

/*
			 * Note the shift key is checked so shift+click on widgets or
			 * nav menu items can just result on focusing on the corresponding
			 * control instead of also navigating to the URL linked to.
			 */
			if ( event.shiftKey ) {
				return;
			}

// Note: It's not relevant to send scroll because sending url message will have the same effect.
			preview.send( 'url', link.prop( 'href' ) );
		},

/**
		 * Handle form submit.
		 *
		 * @since 4.7.0
		 * @access public
		 *
		 * @param {jQuery.Event} event Event.
		 */
		handleFormSubmit: function( event ) {
			var preview = this, urlParser, form;
			urlParser = document.createElement( 'a' );
			form = $( event.target );
			urlParser.href = form.prop( 'action' );

// If the link is not previewable, prevent the browser from navigating to it.
			if ( 'GET' !== form.prop( 'method' ).toUpperCase() || ! api.isLinkPreviewable( urlParser ) ) {
				wp.a11y.speak( api.settings.l10n.formUnpreviewable );
				event.preventDefault();
				return;
			}

/*
			 * If the default wasn't prevented already (in which case the form
			 * submission is already being handled by JS), and if it has a GET
			 * request method, then take the serialized form data and add it as
			 * a query string to the action URL and send this in a url message
			 * to the customizer pane so that it will be loaded. If the form's
			 * action points to a non-previewable URL, the customizer pane's
			 * previewUrl setter will reject it so that the form submission is
			 * a no-op, which is the same behavior as when clicking a link to an
			 * external site in the preview.
			 */
			if ( ! event.isDefaultPrevented() ) {
				if ( urlParser.search.length > 1 ) {
					urlParser.search += '&';
				}
				urlParser.search += form.serialize();
				preview.send( 'url', urlParser.href );
			}

// Prevent default since navigation should be done via sending url message or via JS submit handler.
			event.preventDefault();
		}
	});

/**
	 * Inject the changeset UUID into links in the document.
	 *
	 * @since 4.7.0
	 * @access protected
	 * @access private
	 *
	 * @return {void}
	 */
	api.addLinkPreviewing = function addLinkPreviewing() {
		var linkSelectors = 'a[href], area[href]';

// Inject links into initial document.
		$( document.body ).find( linkSelectors ).each( function() {
			api.prepareLinkPreview( this );
		} );

// Inject links for new elements added to the page.
		if ( 'undefined' !== typeof MutationObserver ) {
			api.mutationObserver = new MutationObserver( function( mutations ) {
				_.each( mutations, function( mutation ) {
					$( mutation.target ).find( linkSelectors ).each( function() {
						api.prepareLinkPreview( this );
					} );
				} );
			} );
			api.mutationObserver.observe( document.documentElement, {
				childList: true,
				subtree: true
			} );
		} else {

// If mutation observers aren't available, fallback to just-in-time injection.
			$( document.documentElement ).on( 'click focus mouseover', linkSelectors, function() {
				api.prepareLinkPreview( this );
			} );
		}
	};

/**
	 * Should the supplied link is previewable.
	 *
	 * @since 4.7.0
	 * @access public
	 *
	 * @param {HTMLAnchorElement|HTMLAreaElement} element Link element.
	 * @param {string} element.search Query string.
	 * @param {string} element.pathname Path.
	 * @param {string} element.host Host.
	 * @param {Object} [options]
	 * @param {Object} [options.allowAdminAjax=false] Allow admin-ajax.php requests.
	 * @return {boolean} Is appropriate for changeset link.
	 */
	api.isLinkPreviewable = function isLinkPreviewable( element, options ) {
		var matchesAllowedUrl, parsedAllowedUrl, args, elementHost;

args = _.extend( {}, { allowAdminAjax: false }, options || {} );

if ( 'javascript:' === element.protocol ) { // jshint ignore:line
			return true;
		}

// Only web URLs can be previewed.
		if ( 'https:' !== element.protocol && 'http:' !== element.protocol ) {
			return false;
		}

elementHost = element.host.replace( /:(80|443)$/, '' );
		parsedAllowedUrl = document.createElement( 'a' );
		matchesAllowedUrl = ! _.isUndefined( _.find( api.settings.url.allowed, function( allowedUrl ) {
			parsedAllowedUrl.href = allowedUrl;
			return parsedAllowedUrl.protocol === element.protocol && parsedAllowedUrl.host.replace( /:(80|443)$/, '' ) === elementHost && 0 === element.pathname.indexOf( parsedAllowedUrl.pathname.replace( /\/$/, '' ) );
		} ) );
		if ( ! matchesAllowedUrl ) {
			return false;
		}

// Skip wp login and signup pages.
		if ( /\/wp-(login|signup)\.php$/.test( element.pathname ) ) {
			return false;
		}

// Allow links to admin ajax as faux frontend URLs.
		if ( /\/wp-admin\/admin-ajax\.php$/.test( element.pathname ) ) {
			return args.allowAdminAjax;
		}

// Disallow links to admin, includes, and content.
		if ( /\/wp-(admin|includes|content)(\/|$)/.test( element.pathname ) ) {
			return false;
		}

return true;
	};

/**
	 * Inject the customize_changeset_uuid query param into links on the frontend.
	 *
	 * @since 4.7.0
	 * @access protected
	 *
	 * @param {HTMLAnchorElement|HTMLAreaElement} element Link element.
	 * @param {string} element.search Query string.
	 * @param {string} element.host Host.
	 * @param {string} element.protocol Protocol.
	 * @return {void}
	 */
	api.prepareLinkPreview = function prepareLinkPreview( element ) {
		var queryParams, $element = $( element );

// Skip elements with no href attribute. Check first to avoid more expensive checks down the road.
        if ( ! element.hasAttribute( 'href' ) ) {
            return;
        }

// Skip links in admin bar.
		if ( $element.closest( '#wpadminbar' ).length ) {
			return;
		}

// Ignore links with href="#", href="#id", or non-HTTP protocols (e.g. javascript: and mailto:).
		if ( '#' === $element.attr( 'href' ).substr( 0, 1 ) || ! /^https?:$/.test( element.protocol ) ) {
			return;
		}

// Make sure links in preview use HTTPS if parent frame uses HTTPS.
		if ( api.settings.channel && 'https' === api.preview.scheme.get() && 'http:' === element.protocol && -1 !== api.settings.url.allowedHosts.indexOf( element.host ) ) {
			element.protocol = 'https:';
		}

// Ignore links with class wp-playlist-caption.
		if ( $element.hasClass( 'wp-playlist-caption' ) ) {
			return;
		}

if ( ! api.isLinkPreviewable( element ) ) {

// Style link as unpreviewable only if previewing in iframe; if previewing on frontend, links will be allowed to work normally.
			if ( api.settings.channel ) {
				$element.addClass( 'customize-unpreviewable' );
			}
			return;
		}
		$element.removeClass( 'customize-unpreviewable' );

queryParams = api.utils.parseQueryString( element.search.substring( 1 ) );
		queryParams.customize_changeset_uuid = api.settings.changeset.uuid;
		if ( api.settings.changeset.autosaved ) {
			queryParams.customize_autosaved = 'on';
		}
		if ( ! api.settings.theme.active ) {
			queryParams.customize_theme = api.settings.theme.stylesheet;
		}
		if ( api.settings.channel ) {
			queryParams.customize_messenger_channel = api.settings.channel;
		}
		element.search = $.param( queryParams );
	};

/**
	 * Inject the changeset UUID into Ajax requests.
	 *
	 * @since 4.7.0
	 * @access protected
	 *
	 * @return {void}
	 */
	api.addRequestPreviewing = function addRequestPreviewing() {

/**
		 * Rewrite Ajax requests to inject customizer state.
		 *
		 * @param {Object} options Options.
		 * @param {string} options.type Type.
		 * @param {string} options.url URL.
		 * @param {Object} originalOptions Original options.
		 * @param {XMLHttpRequest} xhr XHR.
		 * @return {void}
		 */
		var prefilterAjax = function( options, originalOptions, xhr ) {
			var urlParser, queryParams, requestMethod, dirtyValues = {};
			urlParser = document.createElement( 'a' );
			urlParser.href = options.url;

// Abort if the request is not for this site.
			if ( ! api.isLinkPreviewable( urlParser, { allowAdminAjax: true } ) ) {
				return;
			}
			queryParams = api.utils.parseQueryString( urlParser.search.substring( 1 ) );

// Note that _dirty flag will be cleared with changeset updates.
			api.each( function( setting ) {
				if ( setting._dirty ) {
					dirtyValues[ setting.id ] = setting.get();
				}
			} );

if ( ! _.isEmpty( dirtyValues ) ) {
				requestMethod = options.type.toUpperCase();

// Override underlying request method to ensure unsaved changes to changeset can be included (force Backbone.emulateHTTP).
				if ( 'POST' !== requestMethod ) {
					xhr.setRequestHeader( 'X-HTTP-Method-Override', requestMethod );
					queryParams._method = requestMethod;
					options.type = 'POST';
				}

// Amend the post data with the customized values.
				if ( options.data ) {
					options.data += '&';
				} else {
					options.data = '';
				}
				options.data += $.param( {
					customized: JSON.stringify( dirtyValues )
				} );
			}

// Include customized state query params in URL.
			queryParams.customize_changeset_uuid = api.settings.changeset.uuid;
			if ( api.settings.changeset.autosaved ) {
				queryParams.customize_autosaved = 'on';
			}
			if ( ! api.settings.theme.active ) {
				queryParams.customize_theme = api.settings.theme.stylesheet;
			}

// Ensure preview nonce is included with every customized request, to allow post data to be read.
			queryParams.customize_preview_nonce = api.settings.nonce.preview;

urlParser.search = $.param( queryParams );
			options.url = urlParser.href;
		};

$.ajaxPrefilter( prefilterAjax );
	};

/**
	 * Inject changeset UUID into forms, allowing preview to persist through submissions.
	 *
	 * @since 4.7.0
	 * @access protected
	 *
	 * @return {void}
	 */
	api.addFormPreviewing = function addFormPreviewing() {

// Inject inputs for forms in initial document.
		$( document.body ).find( 'form' ).each( function() {
			api.prepareFormPreview( this );
		} );

// Inject inputs for new forms added to the page.
		if ( 'undefined' !== typeof MutationObserver ) {
			api.mutationObserver = new MutationObserver( function( mutations ) {
				_.each( mutations, function( mutation ) {
					$( mutation.target ).find( 'form' ).each( function() {
						api.prepareFormPreview( this );
					} );
				} );
			} );
			api.mutationObserver.observe( document.documentElement, {
				childList: true,
				subtree: true
			} );
		}
	};

/**
	 * Inject changeset into form inputs.
	 *
	 * @since 4.7.0
	 * @access protected
	 *
	 * @param {HTMLFormElement} form Form.
	 * @return {void}
	 */
	api.prepareFormPreview = function prepareFormPreview( form ) {
		var urlParser, stateParams = {};

if ( ! form.action ) {
			form.action = location.href;
		}

urlParser = document.createElement( 'a' );
		urlParser.href = form.action;

// Make sure forms in preview use HTTPS if parent frame uses HTTPS.
		if ( api.settings.channel && 'https' === api.preview.scheme.get() && 'http:' === urlParser.protocol && -1 !== api.settings.url.allowedHosts.indexOf( urlParser.host ) ) {
			urlParser.protocol = 'https:';
			form.action = urlParser.href;
		}

if ( 'GET' !== form.method.toUpperCase() || ! api.isLinkPreviewable( urlParser ) ) {

// Style form as unpreviewable only if previewing in iframe; if previewing on frontend, all forms will be allowed to work normally.
			if ( api.settings.channel ) {
				$( form ).addClass( 'customize-unpreviewable' );
			}
			return;
		}
		$( form ).removeClass( 'customize-unpreviewable' );

stateParams.customize_changeset_uuid = api.settings.changeset.uuid;
		if ( api.settings.changeset.autosaved ) {
			stateParams.customize_autosaved = 'on';
		}
		if ( ! api.settings.theme.active ) {
			stateParams.customize_theme = api.settings.theme.stylesheet;
		}
		if ( api.settings.channel ) {
			stateParams.customize_messenger_channel = api.settings.channel;
		}

_.each( stateParams, function( value, name ) {
			var input = $( form ).find( 'input[name="' + name + '"]' );
			if ( input.length ) {
				input.val( value );
			} else {
				$( form ).prepend( $( '<input>', {
					type: 'hidden',
					name: name,
					value: value
				} ) );
			}
		} );

// Prevent links from breaking out of preview iframe.
		if ( api.settings.channel ) {
			form.target = '_self';
		}
	};

/**
	 * Watch current URL and send keep-alive (heartbeat) messages to the parent.
	 *
	 * Keep the customizer pane notified that the preview is still alive
	 * and that the user hasn't navigated to a non-customized URL.
	 *
	 * @since 4.7.0
	 * @access protected
	 */
	api.keepAliveCurrentUrl = ( function() {
		var previousPathName = location.pathname,
			previousQueryString = location.search.substr( 1 ),
			previousQueryParams = null,
			stateQueryParams = [ 'customize_theme', 'customize_changeset_uuid', 'customize_messenger_channel', 'customize_autosaved' ];

return function keepAliveCurrentUrl() {
			var urlParser, currentQueryParams;

// Short-circuit with keep-alive if previous URL is identical (as is normal case).
			if ( previousQueryString === location.search.substr( 1 ) && previousPathName === location.pathname ) {
				api.preview.send( 'keep-alive' );
				return;
			}

urlParser = document.createElement( 'a' );
			if ( null === previousQueryParams ) {
				urlParser.search = previousQueryString;
				previousQueryParams = api.utils.parseQueryString( previousQueryString );
				_.each( stateQueryParams, function( name ) {
					delete previousQueryParams[ name ];
				} );
			}

// Determine if current URL minus customized state params and URL hash.
			urlParser.href = location.href;
			currentQueryParams = api.utils.parseQueryString( urlParser.search.substr( 1 ) );
			_.each( stateQueryParams, function( name ) {
				delete currentQueryParams[ name ];
			} );

if ( previousPathName !== location.pathname || ! _.isEqual( previousQueryParams, currentQueryParams ) ) {
				urlParser.search = $.param( currentQueryParams );
				urlParser.hash = '';
				api.settings.url.self = urlParser.href;
				api.preview.send( 'ready', {
					currentUrl: api.settings.url.self,
					activePanels: api.settings.activePanels,
					activeSections: api.settings.activeSections,
					activeControls: api.settings.activeControls,
					settingValidities: api.settings.settingValidities
				} );
			} else {
				api.preview.send( 'keep-alive' );
			}
			previousQueryParams = currentQueryParams;
			previousQueryString = location.search.substr( 1 );
			previousPathName = location.pathname;
		};
	} )();

api.settingPreviewHandlers = {

/**
		 * Preview changes to custom logo.
		 *
		 * @param {number} attachmentId Attachment ID for custom logo.
		 * @return {void}
		 */
		custom_logo: function( attachmentId ) {
			$( 'body' ).toggleClass( 'wp-custom-logo', !! attachmentId );
		},

/**
		 * Preview changes to custom css.
		 *
		 * @param {string} value Custom CSS..
		 * @return {void}
		 */
		custom_css: function( value ) {
			$( '#wp-custom-css' ).text( value );
		},

/**
		 * Preview changes to any of the background settings.
		 *
		 * @return {void}
		 */
		background: function() {
			var css = '', settings = {};

_.each( ['color', 'image', 'preset', 'position_x', 'position_y', 'size', 'repeat', 'attachment'], function( prop ) {
				settings[ prop ] = api( 'background_' + prop );
			} );

/*
			 * The body will support custom backgrounds if either the color or image are set.
			 *
			 * See get_body_class() in /wp-includes/post-template.php
			 */
			$( document.body ).toggleClass( 'custom-background', !! ( settings.color() || settings.image() ) );

if ( settings.color() ) {
				css += 'background-color: ' + settings.color() + ';';
			}

if ( settings.image() ) {
				css += 'background-image: url("' + settings.image() + '");';
				css += 'background-size: ' + settings.size() + ';';
				css += 'background-position: ' + settings.position_x() + ' ' + settings.position_y() + ';';
				css += 'background-repeat: ' + settings.repeat() + ';';
				css += 'background-attachment: ' + settings.attachment() + ';';
			}

$( '#custom-background-css' ).text( 'body.custom-background { ' + css + ' }' );
		}
	};

$( function() {
		var bg, setValue, handleUpdatedChangesetUuid;

api.settings = window._wpCustomizeSettings;
		if ( ! api.settings ) {
			return;
		}

api.preview = new api.Preview({
			url: window.location.href,
			channel: api.settings.channel
		});

api.addLinkPreviewing();
		api.addRequestPreviewing();
		api.addFormPreviewing();

/**
		 * Create/update a setting value.
		 *
		 * @param {string}  id            - Setting ID.
		 * @param {*}       value         - Setting value.
		 * @param {boolean} [createDirty] - Whether to create a setting as dirty. Defaults to false.
		 */
		setValue = function( id, value, createDirty ) {
			var setting = api( id );
			if ( setting ) {
				setting.set( value );
			} else {
				createDirty = createDirty || false;
				setting = api.create( id, value, {
					id: id
				} );

// Mark dynamically-created settings as dirty so they will get posted.
				if ( createDirty ) {
					setting._dirty = true;
				}
			}
		};

api.preview.bind( 'settings', function( values ) {
			$.each( values, setValue );
		});

api.preview.trigger( 'settings', api.settings.values );

$.each( api.settings._dirty, function( i, id ) {
			var setting = api( id );
			if ( setting ) {
				setting._dirty = true;
			}
		} );

api.preview.bind( 'setting', function( args ) {
			var createDirty = true;
			setValue.apply( null, args.concat( createDirty ) );
		});

api.preview.bind( 'sync', function( events ) {

/*
			 * Delete any settings that already exist locally which haven't been
			 * modified in the controls while the preview was loading. This prevents
			 * situations where the JS value being synced from the pane may differ
			 * from the PHP-sanitized JS value in the preview which causes the
			 * non-sanitized JS value to clobber the PHP-sanitized value. This
			 * is particularly important for selective refresh partials that
			 * have a fallback refresh behavior since infinite refreshing would
			 * result.
			 */
			if ( events.settings && events['settings-modified-while-loading'] ) {
				_.each( _.keys( events.settings ), function( syncedSettingId ) {
					if ( api.has( syncedSettingId ) && ! events['settings-modified-while-loading'][ syncedSettingId ] ) {
						delete events.settings[ syncedSettingId ];
					}
				} );
			}

$.each( events, function( event, args ) {
				api.preview.trigger( event, args );
			});
			api.preview.send( 'synced' );
		});

api.preview.bind( 'active', function() {
			api.preview.send( 'nonce', api.settings.nonce );

api.preview.send( 'documentTitle', document.title );

// Send scroll in case of loading via non-refresh.
			api.preview.send( 'scroll', $( window ).scrollTop() );
		});

/**
		 * Handle update to changeset UUID.
		 *
		 * @param {string} uuid - UUID.
		 * @return {void}
		 */
		handleUpdatedChangesetUuid = function( uuid ) {
			api.settings.changeset.uuid = uuid;

// Update UUIDs in links and forms.
			$( document.body ).find( 'a[href], area[href]' ).each( function() {
				api.prepareLinkPreview( this );
			} );
			$( document.body ).find( 'form' ).each( function() {
				api.prepareFormPreview( this );
			} );

/*
			 * Replace the UUID in the URL. Note that the wrapped history.replaceState()
			 * will handle injecting the current api.settings.changeset.uuid into the URL,
			 * so this is merely to trigger that logic.
			 */
			if ( history.replaceState ) {
				history.replaceState( currentHistoryState, '', location.href );
			}
		};

api.preview.bind( 'changeset-uuid', handleUpdatedChangesetUuid );

api.preview.bind( 'saved', function( response ) {
			if ( response.next_changeset_uuid ) {
				handleUpdatedChangesetUuid( response.next_changeset_uuid );
			}
			api.trigger( 'saved', response );
		} );

// Update the URLs to reflect the fact we've started autosaving.
		api.preview.bind( 'autosaving', function() {
			if ( api.settings.changeset.autosaved ) {
				return;
			}

api.settings.changeset.autosaved = true; // Start deferring to any autosave once changeset is updated.

$( document.body ).find( 'a[href], area[href]' ).each( function() {
				api.prepareLinkPreview( this );
			} );
			$( document.body ).find( 'form' ).each( function() {
				api.prepareFormPreview( this );
			} );
			if ( history.replaceState ) {
				history.replaceState( currentHistoryState, '', location.href );
			}
		} );

/*
		 * Clear dirty flag for settings when saved to changeset so that they
		 * won't be needlessly included in selective refresh or ajax requests.
		 */
		api.preview.bind( 'changeset-saved', function( data ) {
			_.each( data.saved_changeset_values, function( value, settingId ) {
				var setting = api( settingId );
				if ( setting && _.isEqual( setting.get(), value ) ) {
					setting._dirty = false;
				}
			} );
		} );

api.preview.bind( 'nonce-refresh', function( nonce ) {
			$.extend( api.settings.nonce, nonce );
		} );

/*
		 * Send a message to the parent customize frame with a list of which
		 * containers and controls are active.
		 */
		api.preview.send( 'ready', {
			currentUrl: api.settings.url.self,
			activePanels: api.settings.activePanels,
			activeSections: api.settings.activeSections,
			activeControls: api.settings.activeControls,
			settingValidities: api.settings.settingValidities
		} );

// Send ready when URL changes via JS.
		setInterval( api.keepAliveCurrentUrl, api.settings.timeouts.keepAliveSend );

// Display a loading indicator when preview is reloading, and remove on failure.
		api.preview.bind( 'loading-initiated', function () {
			$( 'body' ).addClass( 'wp-customizer-unloading' );
		});
		api.preview.bind( 'loading-failed', function () {
			$( 'body' ).removeClass( 'wp-customizer-unloading' );
		});

/* Custom Backgrounds */
		bg = $.map( ['color', 'image', 'preset', 'position_x', 'position_y', 'size', 'repeat', 'attachment'], function( prop ) {
			return 'background_' + prop;
		} );

api.when.apply( api, bg ).done( function() {
			$.each( arguments, function() {
				this.bind( api.settingPreviewHandlers.background );
			});
		});

/**
		 * Custom Logo
		 *
		 * Toggle the wp-custom-logo body class when a logo is added or removed.
		 *
		 * @since 4.5.0
		 */
		api( 'custom_logo', function ( setting ) {
			api.settingPreviewHandlers.custom_logo.call( setting, setting.get() );
			setting.bind( api.settingPreviewHandlers.custom_logo );
		} );

api( 'custom_css[' + api.settings.theme.stylesheet + ']', function( setting ) {
			setting.bind( api.settingPreviewHandlers.custom_css );
		} );

api.trigger( 'preview-ready' );
	});

})( wp, jQuery );

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Editing: customize-preview.js

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