Drupal 8.0.0 beta 12. More info: https://www.drupal.org/node/2514176

core/lib/Drupal/Core/Ajax/AddCssCommand.php

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+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Ajax\AddCssCommand.
+ */
+
+namespace Drupal\Core\Ajax;
+
+use Drupal\Core\Ajax\CommandInterface;
+
+/**
+ * An AJAX command for adding css to the page via ajax.
+ *
+ * This command is implemented by Drupal.AjaxCommands.prototype.add_css()
+ * defined in misc/ajax.js.
+ *
+ * @see misc/ajax.js
+ *
+ * @ingroup ajax
+ */
+class AddCssCommand implements CommandInterface {
+
+  /**
+   * A string that contains the styles to be added to the page.
+   *
+   * It should include the wrapping style tag.
+   *
+   * @var string
+   */
+  protected $styles;
+
+  /**
+   * Constructs an AddCssCommand.
+   *
+   * @param string $styles
+   *   A string that contains the styles to be added to the page, including the
+   *   wrapping <style> tag.
+   */
+  public function __construct($styles) {
+    $this->styles = $styles;
+  }
+
+  /**
+   * Implements Drupal\Core\Ajax\CommandInterface:render().
+   */
+  public function render() {
+
+    return array(
+      'command' => 'add_css',
+      'data' => $this->styles,
+    );
+  }
+
+}

core/lib/Drupal/Core/Ajax/AfterCommand.php

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+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Ajax\AfterCommand.
+ */
+
+namespace Drupal\Core\Ajax;
+
+use Drupal\Core\Ajax\InsertCommand;
+
+/**
+ * An AJAX command for calling the jQuery after() method.
+ *
+ * The 'insert/after' command instructs the client to use jQuery's after()
+ * method to insert the given HTML content after each element matched by the
+ * given selector.
+ *
+ * This command is implemented by Drupal.AjaxCommands.prototype.insert()
+ * defined in misc/ajax.js.
+ *
+ * @see http://docs.jquery.com/Manipulation/after#content
+ *
+ * @ingroup ajax
+ */
+class AfterCommand extends InsertCommand {
+
+  /**
+   * Implements Drupal\Core\Ajax\CommandInterface:render().
+   */
+  public function render() {
+
+    return array(
+      'command' => 'insert',
+      'method' => 'after',
+      'selector' => $this->selector,
+      'data' => $this->getRenderedContent(),
+      'settings' => $this->settings,
+    );
+  }
+
+}

core/lib/Drupal/Core/Ajax/AjaxResponse.php

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+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Ajax\AjaxResponse.
+ */
+
+namespace Drupal\Core\Ajax;
+
+use Drupal\Core\Asset\AttachedAssets;
+use Drupal\Core\Render\BubbleableMetadata;
+use Drupal\Core\Render\Renderer;
+use Drupal\Core\Render\AttachmentsInterface;
+use Drupal\Core\Render\AttachmentsTrait;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+use Symfony\Component\HttpFoundation\JsonResponse;
+use Symfony\Component\HttpFoundation\Request;
+use Symfony\Component\HttpFoundation\Response;
+
+/**
+ * JSON response object for AJAX requests.
+ *
+ * @ingroup ajax
+ */
+class AjaxResponse extends JsonResponse implements AttachmentsInterface {
+
+  use AttachmentsTrait;
+
+  /**
+   * The array of ajax commands.
+   *
+   * @var array
+   */
+  protected $commands = array();
+
+  /**
+   * Add an AJAX command to the response.
+   *
+   * @param \Drupal\Core\Ajax\CommandInterface $command
+   *   An AJAX command object implementing CommandInterface.
+   * @param bool $prepend
+   *   A boolean which determines whether the new command should be executed
+   *   before previously added commands. Defaults to FALSE.
+   *
+   * @return AjaxResponse
+   *   The current AjaxResponse.
+   */
+  public function addCommand(CommandInterface $command, $prepend = FALSE) {
+    if ($prepend) {
+      array_unshift($this->commands, $command->render());
+    }
+    else {
+      $this->commands[] = $command->render();
+    }
+    if ($command instanceof CommandWithAttachedAssetsInterface) {
+      $assets = $command->getAttachedAssets();
+      $attachments = [
+        'library' => $assets->getLibraries(),
+        'drupalSettings' => $assets->getSettings(),
+      ];
+      $attachments = BubbleableMetadata::mergeAttachments($this->getAttachments(), $attachments);
+      $this->setAttachments($attachments);
+    }
+
+    return $this;
+  }
+
+  /**
+   * Gets all AJAX commands.
+   *
+   * @return \Drupal\Core\Ajax\CommandInterface[]
+   *   Returns all previously added AJAX commands.
+   */
+  public function &getCommands() {
+    return $this->commands;
+  }
+
+}

core/lib/Drupal/Core/Ajax/AjaxResponseAttachmentsProcessor.php

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+<?php
+/**
+ * @file
+ * Contains \Drupal\Core\Ajax\AjaxResponseAttachmentsProcessor.
+ */
+
+namespace Drupal\Core\Ajax;
+
+use Drupal\Core\Asset\AssetCollectionRendererInterface;
+use Drupal\Core\Asset\AssetResolverInterface;
+use Drupal\Core\Asset\AttachedAssets;
+use Drupal\Core\Config\ConfigFactoryInterface;
+use Drupal\Core\Extension\ModuleHandlerInterface;
+use Drupal\Core\Render\AttachmentsInterface;
+use Drupal\Core\Render\AttachmentsResponseProcessorInterface;
+use Drupal\Core\Render\RendererInterface;
+use Symfony\Component\HttpFoundation\Request;
+use Symfony\Component\HttpFoundation\RequestStack;
+
+/**
+ * Processes attachments of AJAX responses.
+ *
+ * @see \Drupal\Core\Ajax\AjaxResponse
+ * @see \Drupal\Core\Render\MainContent\AjaxRenderer
+ */
+class AjaxResponseAttachmentsProcessor implements AttachmentsResponseProcessorInterface {
+
+  /**
+   * The asset resolver service.
+   *
+   * @var \Drupal\Core\Asset\AssetResolverInterface
+   */
+  protected $assetResolver;
+
+  /**
+   * A config object for the system performance configuration.
+   *
+   * @var \Drupal\Core\Config\Config
+   */
+  protected $config;
+
+  /**
+   * The CSS asset collection renderer service.
+   *
+   * @var \Drupal\Core\Asset\AssetCollectionRendererInterface
+   */
+  protected $cssCollectionRenderer;
+
+  /**
+   * The JS asset collection renderer service.
+   *
+   * @var \Drupal\Core\Asset\AssetCollectionRendererInterface
+   */
+  protected $jsCollectionRenderer;
+
+  /**
+   * The request stack.
+   *
+   * @var \Symfony\Component\HttpFoundation\RequestStack
+   */
+  protected $requestStack;
+
+  /**
+   * The renderer.
+   *
+   * @var \Drupal\Core\Render\RendererInterface
+   */
+  protected $renderer;
+
+  /**
+   * The module handler.
+   *
+   * @var \Drupal\Core\Extension\ModuleHandlerInterface
+   */
+  protected $moduleHandler;
+
+  /**
+   * Constructs a AjaxResponseAttachmentsProcessor object.
+   *
+   * @param \Drupal\Core\Asset\AssetResolverInterface $asset_resolver
+   *   An asset resolver.
+   * @param \Drupal\Core\Config\ConfigFactoryInterface $config_factory
+   *   A config factory for retrieving required config objects.
+   * @param \Drupal\Core\Asset\AssetCollectionRendererInterface $css_collection_renderer
+   *   The CSS asset collection renderer.
+   * @param \Drupal\Core\Asset\AssetCollectionRendererInterface $js_collection_renderer
+   *   The JS asset collection renderer.
+   * @param \Symfony\Component\HttpFoundation\RequestStack $request_stack
+   *   The request stack.
+   * @param \Drupal\Core\Render\RendererInterface $renderer
+   *   The renderer.
+   * @param \Drupal\Core\Extension\ModuleHandlerInterface $module_handler
+   *   The module handler.
+   */
+  public function __construct(AssetResolverInterface $asset_resolver, ConfigFactoryInterface $config_factory, AssetCollectionRendererInterface $css_collection_renderer, AssetCollectionRendererInterface $js_collection_renderer, RequestStack $request_stack, RendererInterface $renderer, ModuleHandlerInterface $module_handler) {
+    $this->assetResolver = $asset_resolver;
+    $this->config = $config_factory->get('system.performance');
+    $this->cssCollectionRenderer = $css_collection_renderer;
+    $this->jsCollectionRenderer = $js_collection_renderer;
+    $this->requestStack = $request_stack;
+    $this->renderer = $renderer;
+    $this->moduleHandler = $module_handler;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function processAttachments(AttachmentsInterface $response) {
+    // @todo Convert to assertion once https://www.drupal.org/node/2408013 lands
+    if (!$response instanceof AjaxResponse) {
+      throw new \InvalidArgumentException('\Drupal\Core\Ajax\AjaxResponse instance expected.');
+    }
+
+    $request = $this->requestStack->getCurrentRequest();
+
+    if ($response->getContent() == '{}') {
+      $response->setData($this->buildAttachmentsCommands($response, $request));
+    }
+
+    return $response;
+  }
+
+  /**
+   * Prepares the AJAX commands to attach assets.
+   *
+   * @param \Drupal\Core\Ajax\AjaxResponse $response
+   *   The AJAX response to update.
+   * @param \Symfony\Component\HttpFoundation\Request $request
+   *   The request object that the AJAX is responding to.
+   *
+   * @return array
+   *   An array of commands ready to be returned as JSON.
+   */
+  protected function buildAttachmentsCommands(AjaxResponse $response, Request $request) {
+    $ajax_page_state = $request->request->get('ajax_page_state');
+
+    // Aggregate CSS/JS if necessary, but only during normal site operation.
+    $optimize_css = !defined('MAINTENANCE_MODE') && $this->config->get('css.preprocess');
+    $optimize_js = !defined('MAINTENANCE_MODE') && $this->config->get('js.preprocess');
+
+    $attachments = $response->getAttachments();
+
+    // Resolve the attached libraries into asset collections.
+    $assets = new AttachedAssets();
+    $assets->setLibraries(isset($attachments['library']) ? $attachments['library'] : [])
+      ->setAlreadyLoadedLibraries(isset($ajax_page_state['libraries']) ? explode(',', $ajax_page_state['libraries']) : [])
+      ->setSettings(isset($attachments['drupalSettings']) ? $attachments['drupalSettings'] : []);
+    $css_assets = $this->assetResolver->getCssAssets($assets, $optimize_css);
+    list($js_assets_header, $js_assets_footer) = $this->assetResolver->getJsAssets($assets, $optimize_js);
+
+    // Render the HTML to load these files, and add AJAX commands to insert this
+    // HTML in the page. Settings are handled separately, afterwards.
+    $settings = [];
+    if (isset($js_assets_header['drupalSettings'])) {
+      $settings = $js_assets_header['drupalSettings']['data'];
+      unset($js_assets_header['drupalSettings']);
+    }
+    if (isset($js_assets_footer['drupalSettings'])) {
+      $settings = $js_assets_footer['drupalSettings']['data'];
+      unset($js_assets_footer['drupalSettings']);
+    }
+
+    // Prepend commands to add the assets, preserving their relative order.
+    $resource_commands = array();
+    if ($css_assets) {
+      $css_render_array = $this->cssCollectionRenderer->render($css_assets);
+      $resource_commands[] = new AddCssCommand($this->renderer->renderPlain($css_render_array));
+    }
+    if ($js_assets_header) {
+      $js_header_render_array = $this->jsCollectionRenderer->render($js_assets_header);
+      $resource_commands[] = new PrependCommand('head', $this->renderer->renderPlain($js_header_render_array));
+    }
+    if ($js_assets_footer) {
+      $js_footer_render_array = $this->jsCollectionRenderer->render($js_assets_footer);
+      $resource_commands[] = new AppendCommand('body', $this->renderer->renderPlain($js_footer_render_array));
+    }
+    foreach (array_reverse($resource_commands) as $resource_command) {
+      $response->addCommand($resource_command, TRUE);
+    }
+
+    // Prepend a command to merge changes and additions to drupalSettings.
+    if (!empty($settings)) {
+      // During Ajax requests basic path-specific settings are excluded from
+      // new drupalSettings values. The original page where this request comes
+      // from already has the right values. An Ajax request would update them
+      // with values for the Ajax request and incorrectly override the page's
+      // values.
+      // @see system_js_settings_alter()
+      unset($settings['path']);
+      $response->addCommand(new SettingsCommand($settings, TRUE), TRUE);
+    }
+
+    $commands = $response->getCommands();
+    $this->moduleHandler->alter('ajax_render', $commands);
+
+    return $commands;
+  }
+
+}

core/lib/Drupal/Core/Ajax/AlertCommand.php

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+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Ajax\AlertCommand.
+ */
+
+namespace Drupal\Core\Ajax;
+
+use Drupal\Core\Ajax\CommandInterface;
+
+/**
+ * AJAX command for a javascript alert box.
+ *
+ * @ingroup ajax
+ */
+class AlertCommand implements CommandInterface {
+
+  /**
+   * The text to be displayed in the alert box.
+   *
+   * @var string
+   */
+  protected $text;
+
+  /**
+   * Constructs an AlertCommand object.
+   *
+   * @param string $text
+   *   The text to be displayed in the alert box.
+   */
+  public function __construct($text) {
+    $this->text = $text;
+  }
+
+  /**
+   * Implements Drupal\Core\Ajax\CommandInterface:render().
+   */
+  public function render() {
+
+    return array(
+      'command' => 'alert',
+      'text' => $this->text,
+    );
+  }
+
+}

core/lib/Drupal/Core/Ajax/AppendCommand.php

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+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Ajax\AppendCommand.
+ */
+
+namespace Drupal\Core\Ajax;
+
+use Drupal\Core\Ajax\InsertCommand;
+
+/**
+ * An AJAX command for calling the jQuery append() method.
+ *
+ * The 'insert/append' command instructs the client to use jQuery's append()
+ * method to append the given HTML content to the inside of each element matched
+ * by the given selector.
+ *
+ * This command is implemented by Drupal.AjaxCommands.prototype.insert()
+ * defined in misc/ajax.js.
+ *
+ * @see http://docs.jquery.com/Manipulation/append#content
+ *
+ * @ingroup ajax
+ */
+class AppendCommand extends InsertCommand {
+
+  /**
+   * Implements Drupal\Core\Ajax\CommandInterface:render().
+   */
+  public function render() {
+
+    return array(
+      'command' => 'insert',
+      'method' => 'append',
+      'selector' => $this->selector,
+      'data' => $this->getRenderedContent(),
+      'settings' => $this->settings,
+    );
+  }
+
+}

core/lib/Drupal/Core/Ajax/BeforeCommand.php

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+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Ajax\BeforeCommand.
+ */
+
+namespace Drupal\Core\Ajax;
+
+use Drupal\Core\Ajax\InsertCommand;
+
+/**
+ * An AJAX command for calling the jQuery before() method.
+ *
+ * The 'insert/before' command instructs the client to use jQuery's before()
+ * method to insert the given HTML content before each of elements matched by
+ * the given selector.
+ *
+ * This command is implemented by Drupal.AjaxCommands.prototype.insert()
+ * defined in misc/ajax.js.
+ *
+ * @see http://docs.jquery.com/Manipulation/before#content
+ *
+ * @ingroup ajax
+ */
+class BeforeCommand extends InsertCommand {
+
+  /**
+   * Implements Drupal\Core\Ajax\CommandInterface:render().
+   */
+  public function render() {
+
+    return array(
+      'command' => 'insert',
+      'method' => 'before',
+      'selector' => $this->selector,
+      'data' => $this->getRenderedContent(),
+      'settings' => $this->settings,
+    );
+  }
+
+}

core/lib/Drupal/Core/Ajax/ChangedCommand.php

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+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Ajax\ChangedCommand.
+ */
+
+namespace Drupal\Core\Ajax;
+
+use Drupal\Core\Ajax\CommandInterface;
+
+/**
+ * An AJAX command for marking HTML elements as changed.
+ *
+ * This command instructs the client to mark each of the elements matched by the
+ * given selector as 'ajax-changed'.
+ *
+ * This command is implemented by Drupal.AjaxCommands.prototype.changed()
+ * defined in misc/ajax.js.
+ *
+ * @ingroup ajax
+ */
+class ChangedCommand implements CommandInterface {
+
+  /**
+   * A CSS selector string.
+   *
+   * If the command is a response to a request from an #ajax form element then
+   * this value can be NULL.
+   *
+   * @var string
+   */
+  protected $selector;
+
+  /**
+   * An optional CSS selector for elements to which asterisks will be appended.
+   *
+   * @var string
+   */
+  protected $asterisk;
+
+  /**
+   * Constructs a ChangedCommand object.
+   *
+   * @param string $selector
+   *   CSS selector for elements to be marked as changed.
+   * @param string $asterisk
+   *   CSS selector for elements to which an asterisk will be appended.
+   */
+  public function __construct($selector, $asterisk = '') {
+    $this->selector = $selector;
+    $this->asterisk = $asterisk;
+  }
+
+  /**
+   * Implements Drupal\Core\Ajax\CommandInterface:render().
+   */
+  public function render() {
+
+    return array(
+      'command' => 'changed',
+      'selector' => $this->selector,
+      'asterisk' => $this->asterisk,
+    );
+  }
+
+}

core/lib/Drupal/Core/Ajax/CloseDialogCommand.php

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+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Ajax\CloseDialogCommand.
+ */
+
+namespace Drupal\Core\Ajax;
+
+/**
+ * Defines an AJAX command that closes the current active dialog.
+ *
+ * @ingroup ajax
+ */
+class CloseDialogCommand implements CommandInterface {
+
+  /**
+   * A CSS selector string of the dialog to close.
+   *
+   * @var string
+   */
+  protected $selector;
+
+  /**
+   * Whether to persist the dialog in the DOM or not.
+   *
+   * @var bool
+   */
+  protected $persist;
+
+  /**
+   * Constructs a CloseDialogCommand object.
+   *
+   * @param string $selector
+   *   A CSS selector string of the dialog to close.
+   * @param bool $persist
+   *   (optional) Whether to persist the dialog in the DOM or not.
+   */
+  public function __construct($selector = NULL, $persist = FALSE) {
+    $this->selector = $selector ? $selector : '#drupal-modal';
+    $this->persist = $persist;
+  }
+
+  /**
+   * Implements \Drupal\Core\Ajax\CommandInterface::render().
+   */
+  public function render() {
+    return array(
+      'command' => 'closeDialog',
+      'selector' => $this->selector,
+      'persist' => $this->persist,
+    );
+  }
+}

core/lib/Drupal/Core/Ajax/CloseModalDialogCommand.php

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+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Ajax\CloseModalDialogCommand.
+ */
+
+namespace Drupal\Core\Ajax;
+
+use Drupal\Core\Ajax\CloseDialogCommand;
+
+/**
+ * Defines an AJAX command that closes the currently visible modal dialog.
+ *
+ * @ingroup ajax
+ */
+class CloseModalDialogCommand extends CloseDialogCommand {
+
+  /**
+   * Constructs a CloseModalDialogCommand object.
+   *
+   * @param bool $persist
+   *   (optional) Whether to persist the dialog in the DOM or not.
+   */
+  public function __construct($persist = FALSE) {
+    $this->selector = '#drupal-modal';
+    $this->persist = $persist;
+  }
+
+}

core/lib/Drupal/Core/Ajax/CommandInterface.php

@@ -0,0 +1,24 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Ajax\CommandInterface.
+ */
+
+namespace Drupal\Core\Ajax;
+
+/**
+ * AJAX command interface.
+ *
+ * All AJAX commands passed to AjaxResponse objects should implement these
+ * methods.
+ *
+ * @ingroup ajax
+ */
+interface CommandInterface {
+
+  /**
+   * Return an array to be run through json_encode and sent to the client.
+   */
+  public function render();
+}

core/lib/Drupal/Core/Ajax/CommandWithAttachedAssetsInterface.php

@@ -0,0 +1,28 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Ajax\CommandWithAttachedAssetsInterface.
+ */
+
+namespace Drupal\Core\Ajax;
+
+/**
+ * Interface for Ajax commands that render content and attach assets.
+ *
+ * All Ajax commands that render HTML should implement these methods
+ * to be able to return attached assets to the calling AjaxResponse object.
+ *
+ * @ingroup ajax
+ */
+interface CommandWithAttachedAssetsInterface {
+
+  /**
+   * Gets the attached assets.
+   *
+   * @return \Drupal\Core\Asset\AttachedAssets|null
+   *   The attached assets for this command.
+   */
+  public function getAttachedAssets();
+
+}

core/lib/Drupal/Core/Ajax/CommandWithAttachedAssetsTrait.php

@@ -0,0 +1,57 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Ajax\CommandWithAttachedAssetsTrait.
+ */
+
+namespace Drupal\Core\Ajax;
+
+use Drupal\Core\Asset\AttachedAssets;
+
+/**
+ * Trait for Ajax commands that render content and attach assets.
+ *
+ * @ingroup ajax
+ */
+trait CommandWithAttachedAssetsTrait {
+
+  /**
+   * The attached assets for this Ajax command.
+   *
+   * @var \Drupal\Core\Asset\AttachedAssets
+   */
+  protected $attachedAssets;
+
+  /**
+   * Processes the content for output.
+   *
+   * If content is a render array, it may contain attached assets to be
+   * processed.
+   *
+   * @return string
+   *   HTML rendered content.
+   */
+  protected function getRenderedContent() {
+    $this->attachedAssets = new AttachedAssets();
+    if (is_array($this->content)) {
+      $html = \Drupal::service('renderer')->renderRoot($this->content);
+      $this->attachedAssets = AttachedAssets::createFromRenderArray($this->content);
+      return $html;
+    }
+    else {
+      return $this->content;
+    }
+  }
+
+  /**
+   * Gets the attached assets.
+   *
+   * @return \Drupal\Core\Asset\AttachedAssets|null
+   *   The attached assets for this command.
+   */
+  public function getAttachedAssets() {
+    return $this->attachedAssets;
+  }
+
+}

core/lib/Drupal/Core/Ajax/CssCommand.php

@@ -0,0 +1,84 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Ajax\CssCommand.
+ */
+
+namespace Drupal\Core\Ajax;
+
+use Drupal\Core\Ajax\CommandInterface;
+
+/**
+ * An AJAX command for calling the jQuery css() method.
+ *
+ * The 'css' command will instruct the client to use the jQuery css() method to
+ * apply the CSS arguments to elements matched by the given selector.
+ *
+ * This command is implemented by Drupal.AjaxCommands.prototype.css() defined
+ * in misc/ajax.js.
+ *
+ * @see http://docs.jquery.com/CSS/css#properties
+ *
+ * @ingroup ajax
+ */
+class CssCommand implements CommandInterface {
+
+  /**
+   * A CSS selector string.
+   *
+   * If the command is a response to a request from an #ajax form element then
+   * this value can be NULL.
+   *
+   * @var string
+   */
+  protected $selector;
+
+  /**
+   * An array of property/value pairs to set in the CSS for the selector.
+   *
+   * @var array
+   */
+  protected $css = array();
+
+  /**
+   * Constructs a CssCommand object.
+   *
+   * @param string $selector
+   *   A CSS selector for elements to which the CSS will be applied.
+   * @param array $css
+   *   An array of CSS property/value pairs to set.
+   */
+  public function __construct($selector, array $css = array()) {
+    $this->selector = $selector;
+    $this->css = $css;
+  }
+
+  /**
+   * Adds a property/value pair to the CSS to be added to this element.
+   *
+   * @param $property
+   *   The CSS property to be changed.
+   * @param $value
+   *   The new value of the CSS property.
+   *
+   * @return $this
+   */
+  public function setProperty($property, $value) {
+    $this->css[$property] = $value;
+    return $this;
+  }
+
+  /**
+   * Implements Drupal\Core\Ajax\CommandInterface:render().
+   */
+  public function render() {
+
+    return array(
+      'command' => 'css',
+      'selector' => $this->selector,
+      'argument' => $this->css,
+    );
+  }
+
+}

core/lib/Drupal/Core/Ajax/DataCommand.php

@@ -0,0 +1,81 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Ajax\DataCommand.
+ */
+
+namespace Drupal\Core\Ajax;
+
+use Drupal\Core\Ajax\CommandInterface;
+
+/**
+ * An AJAX command for implementing jQuery's data() method.
+ *
+ * This instructs the client to attach the name=value pair of data to the
+ * selector via jQuery's data cache.
+ *
+ * This command is implemented by Drupal.AjaxCommands.prototype.data() defined
+ * in misc/ajax.js.
+ *
+ * @ingroup ajax
+ */
+class DataCommand implements CommandInterface {
+
+  /**
+   * A CSS selector string for elements to which data will be attached.
+   *
+   * If the command is a response to a request from an #ajax form element then
+   * this value can be NULL.
+   *
+   * @var string
+   */
+  protected $selector;
+
+  /**
+   * The key of the data attached to elements matched by the selector.
+   *
+   * @var string
+   */
+  protected $name;
+
+  /**
+   * The value of the data to be attached to elements matched by the selector.
+   *
+   * The data is not limited to strings; it can be any format.
+   *
+   * @var mixed
+   */
+  protected $value;
+
+  /**
+   * Constructs a DataCommand object.
+   *
+   * @param string $selector
+   *   A CSS selector for the elements to which the data will be attached.
+   * @param string $name
+   *   The key of the data to be attached to elements matched by the selector.
+   * @param type $value
+   *   The value of the data to be attached to elements matched by the selector.
+   */
+  public function __construct($selector, $name, $value) {
+    $this->selector = $selector;
+    $this->name = $name;
+    $this->value = $value;
+  }
+
+  /**
+   * Implements Drupal\Core\Ajax\CommandInterface:render().
+   */
+  public function render() {
+
+    return array(
+      'command' => 'data',
+      'selector' => $this->selector,
+      'name' => $this->name,
+      'value' => $this->value,
+    );
+  }
+
+}
+

core/lib/Drupal/Core/Ajax/HtmlCommand.php

@@ -0,0 +1,42 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Ajax\HtmlCommand.
+ */
+
+namespace Drupal\Core\Ajax;
+
+use Drupal\Core\Ajax\InsertCommand;
+
+/**
+ * AJAX command for calling the jQuery html() method.
+ *
+ * The 'insert/html' command instructs the client to use jQuery's html() method
+ * to set the HTML content of each element matched by the given selector while
+ * leaving the outer tags intact.
+ *
+ * This command is implemented by Drupal.AjaxCommands.prototype.insert()
+ * defined in misc/ajax.js.
+ *
+ * @see http://docs.jquery.com/Attributes/html#val
+ *
+ * @ingroup ajax
+ */
+class HtmlCommand extends InsertCommand {
+
+  /**
+   * Implements Drupal\Core\Ajax\CommandInterface:render().
+   */
+  public function render() {
+
+    return array(
+      'command' => 'insert',
+      'method' => 'html',
+      'selector' => $this->selector,
+      'data' => $this->getRenderedContent(),
+      'settings' => $this->settings,
+    );
+  }
+
+}

core/lib/Drupal/Core/Ajax/InsertCommand.php

@@ -0,0 +1,85 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Ajax\InsertCommand.
+ */
+
+namespace Drupal\Core\Ajax;
+
+use Drupal\Core\Ajax\CommandInterface;
+
+/**
+ * Generic AJAX command for inserting content.
+ *
+ * This command instructs the client to insert the given HTML using whichever
+ * jQuery DOM manipulation method has been specified in the #ajax['method']
+ * variable of the element that triggered the request.
+ *
+ * This command is implemented by Drupal.AjaxCommands.prototype.insert()
+ * defined in misc/ajax.js.
+ *
+ * @ingroup ajax
+ */
+class InsertCommand implements CommandInterface, CommandWithAttachedAssetsInterface {
+
+  use CommandWithAttachedAssetsTrait;
+
+  /**
+   * A CSS selector string.
+   *
+   * If the command is a response to a request from an #ajax form element then
+   * this value can be NULL.
+   *
+   * @var string
+   */
+  protected $selector;
+
+  /**
+   * The content for the matched element(s).
+   *
+   * Either a render array or an HTML string.
+   *
+   * @var string|array
+   */
+  protected $content;
+
+  /**
+   * A settings array to be passed to any any attached JavaScript behavior.
+   *
+   * @var array
+   */
+  protected $settings;
+
+  /**
+   * Constructs an InsertCommand object.
+   *
+   * @param string $selector
+   *   A CSS selector.
+   * @param string|array $content
+   *   The content that will be inserted in the matched element(s), either a
+   *   render array or an HTML string.
+   * @param array $settings
+   *   An array of JavaScript settings to be passed to any attached behaviors.
+   */
+  public function __construct($selector, $content, array $settings = NULL) {
+    $this->selector = $selector;
+    $this->content = $content;
+    $this->settings = $settings;
+  }
+
+  /**
+   * Implements Drupal\Core\Ajax\CommandInterface:render().
+   */
+  public function render() {
+
+    return array(
+      'command' => 'insert',
+      'method' => NULL,
+      'selector' => $this->selector,
+      'data' => $this->getRenderedContent(),
+      'settings' => $this->settings,
+    );
+  }
+
+}

core/lib/Drupal/Core/Ajax/InvokeCommand.php

@@ -0,0 +1,80 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Ajax\InvokeCommand.
+ */
+
+namespace Drupal\Core\Ajax;
+
+use Drupal\Core\Ajax\CommandInterface;
+
+/**
+ * AJAX command for invoking an arbitrary jQuery method.
+ *
+ * The 'invoke' command will instruct the client to invoke the given jQuery
+ * method with the supplied arguments on the elements matched by the given
+ * selector. Intended for simple jQuery commands, such as attr(), addClass(),
+ * removeClass(), toggleClass(), etc.
+ *
+ * This command is implemented by Drupal.AjaxCommands.prototype.invoke()
+ * defined in misc/ajax.js.
+ *
+ * @ingroup ajax
+ */
+class InvokeCommand implements CommandInterface {
+
+  /**
+   * A CSS selector string.
+   *
+   * If the command is a response to a request from an #ajax form element then
+   * this value can be NULL.
+   *
+   * @var string
+   */
+  protected $selector;
+
+  /**
+   * A jQuery method to invoke.
+   *
+   * @var string
+   */
+  protected $method;
+
+  /**
+   * An optional list of arguments to pass to the method.
+   *
+   * @var array
+   */
+  protected $arguments;
+
+  /**
+   * Constructs an InvokeCommand object.
+   *
+   * @param string $selector
+   *   A jQuery selector.
+   * @param string $method
+   *   The name of a jQuery method to invoke.
+   * @param array $arguments
+   *   An optional array of arguments to pass to the method.
+   */
+  public function __construct($selector, $method, array $arguments = array()) {
+    $this->selector = $selector;
+    $this->method = $method;
+    $this->arguments = $arguments;
+  }
+
+  /**
+   * Implements Drupal\Core\Ajax\CommandInterface:render().
+   */
+  public function render() {
+
+    return array(
+      'command' => 'invoke',
+      'selector' => $this->selector,
+      'method' => $this->method,
+      'args' => $this->arguments,
+    );
+  }
+
+}

core/lib/Drupal/Core/Ajax/OpenDialogCommand.php

@@ -0,0 +1,144 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Ajax\OpenDialogCommand.
+ */
+
+namespace Drupal\Core\Ajax;
+
+use Drupal\Core\Ajax\CommandInterface;
+
+/**
+ * Defines an AJAX command to open certain content in a dialog.
+ *
+ * @ingroup ajax
+ */
+class OpenDialogCommand implements CommandInterface, CommandWithAttachedAssetsInterface {
+
+  use CommandWithAttachedAssetsTrait;
+
+  /**
+   * The selector of the dialog.
+   *
+   * @var string
+   */
+  protected $selector;
+
+  /**
+   * The title of the dialog.
+   *
+   * @var string
+   */
+  protected $title;
+
+  /**
+   * The content for the dialog.
+   *
+   * Either a render array or an HTML string.
+   *
+   * @var string|array
+   */
+  protected $content;
+
+  /**
+   * Stores dialog-specific options passed directly to jQuery UI dialogs. Any
+   * jQuery UI option can be used. See http://api.jqueryui.com/dialog.
+   *
+   * @var array
+   */
+  protected $dialogOptions;
+
+  /**
+   * Custom settings that will be passed to the Drupal behaviors on the content
+   * of the dialog.
+   *
+   * @var array
+   */
+  protected $settings;
+
+  /**
+   * Constructs an OpenDialogCommand object.
+   *
+   * @param string $selector
+   *   The selector of the dialog.
+   * @param string $title
+   *   The title of the dialog.
+   * @param string|array $content
+   *   The content that will be placed in the dialog, either a render array
+   *   or an HTML string.
+   * @param array $dialog_options
+   *   (optional) Options to be passed to the dialog implementation. Any
+   *   jQuery UI option can be used. See http://api.jqueryui.com/dialog.
+   * @param array|null $settings
+   *   (optional) Custom settings that will be passed to the Drupal behaviors
+   *   on the content of the dialog. If left empty, the settings will be
+   *   populated automatically from the current request.
+   */
+  public function __construct($selector, $title, $content, array $dialog_options = array(), $settings = NULL) {
+    $dialog_options += array('title' => $title);
+    $this->selector = $selector;
+    $this->content = $content;
+    $this->dialogOptions = $dialog_options;
+    $this->settings = $settings;
+  }
+
+  /**
+   * Returns the dialog options.
+   *
+   * @return array
+   */
+  public function getDialogOptions() {
+    return $this->dialogOptions;
+  }
+
+  /**
+   * Sets the dialog options array.
+   *
+   * @param array $dialog_options
+   *   Options to be passed to the dialog implementation. Any jQuery UI option
+   *   can be used. See http://api.jqueryui.com/dialog.
+   */
+  public function setDialogOptions($dialog_options) {
+    $this->dialogOptions = $dialog_options;
+  }
+
+  /**
+   * Sets a single dialog option value.
+   *
+   * @param string $key
+   *   Key of the dialog option. Any jQuery UI option can be used.
+   *   See http://api.jqueryui.com/dialog.
+   * @param mixed $value
+   *   Option to be passed to the dialog implementation.
+   */
+  public function setDialogOption($key, $value) {
+    $this->dialogOptions[$key] = $value;
+  }
+
+  /**
+   * Sets the dialog title (an alias of setDialogOptions).
+   *
+   * @param string $title
+   *   The new title of the dialog.
+   */
+  public function setDialogTitle($title) {
+    $this->setDialogOptions('title', $title);
+  }
+
+  /**
+   * Implements \Drupal\Core\Ajax\CommandInterface:render().
+   */
+  public function render() {
+    // For consistency ensure the modal option is set to TRUE or FALSE.
+    $this->dialogOptions['modal'] = isset($this->dialogOptions['modal']) && $this->dialogOptions['modal'];
+    return array(
+      'command' => 'openDialog',
+      'selector' => $this->selector,
+      'settings' => $this->settings,
+      'data' => $this->getRenderedContent(),
+      'dialogOptions' => $this->dialogOptions,
+    );
+  }
+
+}

core/lib/Drupal/Core/Ajax/OpenModalDialogCommand.php

@@ -0,0 +1,43 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Ajax\OpenModalDialogCommand.
+ */
+
+namespace Drupal\Core\Ajax;
+
+use Drupal\Core\Ajax\OpenDialogCommand;
+
+/**
+ * Defines an AJAX command to open certain content in a dialog in a modal dialog.
+ *
+ * @ingroup ajax
+ */
+class OpenModalDialogCommand extends OpenDialogCommand {
+  /**
+   * Constructs an OpenModalDialog object.
+   *
+   * The modal dialog differs from the normal modal provided by
+   * OpenDialogCommand in that a modal prevents other interactions on the page
+   * until the modal has been completed. Drupal provides a built-in modal for
+   * this purpose, so no selector needs to be provided.
+   *
+   * @param string $title
+   *   The title of the dialog.
+   * @param string|array $content
+   *   The content that will be placed in the dialog, either a render array
+   *   or an HTML string.
+   * @param array $dialog_options
+   *   (optional) Settings to be passed to the dialog implementation. Any
+   *   jQuery UI option can be used. See http://api.jqueryui.com/dialog.
+   * @param array|null $settings
+   *   (optional) Custom settings that will be passed to the Drupal behaviors
+   *   on the content of the dialog. If left empty, the settings will be
+   *   populated automatically from the current request.
+   */
+  public function __construct($title, $content, array $dialog_options = array(), $settings = NULL) {
+    $dialog_options['modal'] = TRUE;
+    parent::__construct('#drupal-modal', $title, $content, $dialog_options, $settings);
+  }
+}

core/lib/Drupal/Core/Ajax/PrependCommand.php

@@ -0,0 +1,42 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Ajax\PrependCommand.
+ */
+
+namespace Drupal\Core\Ajax;
+
+use Drupal\Core\Ajax\InsertCommand;
+
+/**
+ * AJAX command for calling the jQuery insert() method.
+ *
+ * The 'insert/prepend' command instructs the client to use jQuery's prepend()
+ * method to prepend the given HTML content to the inside each element matched
+ * by the given selector.
+ *
+ * This command is implemented by Drupal.AjaxCommands.prototype.insert()
+ * defined in misc/ajax.js.
+ *
+ * @see http://docs.jquery.com/Manipulation/prepend#content
+ *
+ * @ingroup ajax
+ */
+class PrependCommand extends InsertCommand {
+
+  /**
+   * Implements Drupal\Core\Ajax\CommandInterface:render().
+   */
+  public function render() {
+
+    return array(
+      'command' => 'insert',
+      'method' => 'prepend',
+      'selector' => $this->selector,
+      'data' => $this->getRenderedContent(),
+      'settings' => $this->settings,
+    );
+  }
+
+}

core/lib/Drupal/Core/Ajax/RedirectCommand.php

@@ -0,0 +1,47 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Ajax\RedirectCommand.
+ */
+
+namespace Drupal\Core\Ajax;
+
+use Drupal\Core\Ajax\CommandInterface;
+
+/**
+ * Defines an AJAX command to set the window.location, loading that URL.
+ *
+ * @ingroup ajax
+ */
+class RedirectCommand implements CommandInterface {
+
+  /**
+   * The URL that will be loaded into window.location.
+   *
+   * @var string
+   */
+  protected $url;
+
+  /**
+   * Constructs an RedirectCommand object.
+   *
+   * @param string $url
+   *   The URL that will be loaded into window.location. This should be a full
+   *   URL.
+   */
+  public function __construct($url) {
+    $this->url = $url;
+  }
+
+  /**
+   * Implements \Drupal\Core\Ajax\CommandInterface:render().
+   */
+  public function render() {
+    return array(
+      'command' => 'redirect',
+      'url' => $this->url,
+    );
+  }
+
+}

core/lib/Drupal/Core/Ajax/RemoveCommand.php

@@ -0,0 +1,55 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Ajax\RemoveCommand.
+ */
+
+namespace Drupal\Core\Ajax;
+
+use Drupal\Core\Ajax\CommandInterface;
+
+/**
+ * AJAX command for calling the jQuery remove() method.
+ *
+ * The 'remove' command instructs the client to use jQuery's remove() method
+ * to remove each of elements matched by the given selector, and everything
+ * within them.
+ *
+ * This command is implemented by Drupal.AjaxCommands.prototype.remove()
+ * defined in misc/ajax.js.
+ *
+ * @see http://docs.jquery.com/Manipulation/remove#expr
+ *
+ * @ingroup ajax
+ */
+class RemoveCommand Implements CommandInterface {
+
+  /**
+   * The CSS selector for the element(s) to be removed.
+   *
+   * @var string
+   */
+  protected $selector;
+
+  /**
+   * Constructs a RemoveCommand object.
+   *
+   * @param string $selector
+   *
+   */
+  public function __construct($selector) {
+    $this->selector = $selector;
+  }
+
+  /**
+   * Implements Drupal\Core\Ajax\CommandInterface:render().
+   */
+  public function render() {
+    return array(
+      'command' => 'remove',
+      'selector' => $this->selector,
+    );
+  }
+
+}

core/lib/Drupal/Core/Ajax/ReplaceCommand.php

@@ -0,0 +1,43 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Ajax\ReplaceCommand.
+ */
+
+namespace Drupal\Core\Ajax;
+
+use Drupal\Core\Ajax\InsertCommand;
+
+/**
+ * AJAX command for calling the jQuery replace() method.
+ *
+ * The 'insert/replaceWith' command instructs the client to use jQuery's
+ * replaceWith() method to replace each element matched matched by the given
+ * selector with the given HTML.
+ *
+ * This command is implemented by Drupal.AjaxCommands.prototype.insert()
+ * defined in misc/ajax.js.
+ *
+ * See
+ * @link http://docs.jquery.com/Manipulation/replaceWith#content jQuery replaceWith command @endlink
+ *
+ * @ingroup ajax
+ */
+class ReplaceCommand extends InsertCommand {
+
+  /**
+   * Implements Drupal\Core\Ajax\CommandInterface:render().
+   */
+  public function render() {
+
+    return array(
+      'command' => 'insert',
+      'method' => 'replaceWith',
+      'selector' => $this->selector,
+      'data' => $this->getRenderedContent(),
+      'settings' => $this->settings,
+    );
+  }
+
+}

core/lib/Drupal/Core/Ajax/RestripeCommand.php

@@ -0,0 +1,56 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Ajax\RestripeCommand.
+ */
+
+namespace Drupal\Core\Ajax;
+
+use Drupal\Core\Ajax\CommandInterface;
+
+/**
+ * AJAX command for resetting the striping on a table.
+ *
+ * The 'restripe' command instructs the client to restripe a table. This is
+ * usually used after a table has been modified by a replace or append command.
+ *
+ * This command is implemented by Drupal.AjaxCommands.prototype.restripe()
+ * defined in misc/ajax.js.
+ *
+ * @ingroup ajax
+ */
+class RestripeCommand implements CommandInterface {
+
+  /**
+   * A CSS selector string.
+   *
+   * If the command is a response to a request from an #ajax form element then
+   * this value can be NULL.
+   *
+   * @var string
+   */
+  protected $selector;
+
+  /**
+   * Constructs a RestripeCommand object.
+   *
+   * @param string $selector
+   *   A CSS selector for the table to be restriped.
+   */
+  public function __construct($selector) {
+    $this->selector = $selector;
+  }
+
+  /**
+   * Implements Drupal\Core\Ajax\CommandInterface:render().
+   */
+  public function render() {
+
+    return array(
+      'command' => 'restripe',
+      'selector' => $this->selector,
+    );
+  }
+
+}

core/lib/Drupal/Core/Ajax/SetDialogOptionCommand.php

@@ -0,0 +1,68 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Ajax\SetDialogOptionCommand.
+ */
+
+namespace Drupal\Core\Ajax;
+
+/**
+ * Defines an AJAX command that sets jQuery UI dialog properties.
+ *
+ * @ingroup ajax
+ */
+class SetDialogOptionCommand implements CommandInterface {
+
+  /**
+   * A CSS selector string.
+   *
+   * @var string
+   */
+  protected $selector;
+
+  /**
+   * A jQuery UI dialog option name.
+   *
+   * @var string
+   */
+  protected $optionName;
+
+  /**
+   * A jQuery UI dialog option value.
+   *
+   * @var mixed
+   */
+  protected $optionValue;
+
+  /**
+   * Constructs a SetDialogOptionCommand object.
+   *
+   * @param string $selector
+   *   The selector of the dialog whose title will be set. If set to an empty
+   *   value, the default modal dialog will be selected.
+   * @param string $option_name
+   *   The name of the option to set. May be any jQuery UI dialog option.
+   *   See http://api.jqueryui.com/dialog.
+   * @param mixed $option_value
+   *   The value of the option to be passed to the dialog.
+   */
+  public function __construct($selector, $option_name, $option_value) {
+    $this->selector = $selector ? $selector : '#drupal-modal';
+    $this->optionName = $option_name;
+    $this->optionValue = $option_value;
+  }
+
+  /**
+   * Implements \Drupal\Core\Ajax\CommandInterface::render().
+   */
+  public function render() {
+    return array(
+      'command' => 'setDialogOption',
+      'selector' => $this->selector,
+      'optionName' => $this->optionName,
+      'optionValue' => $this->optionValue,
+    );
+  }
+
+}

core/lib/Drupal/Core/Ajax/SetDialogTitleCommand.php

@@ -0,0 +1,33 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Ajax\SetDialogTitleCommand.
+ */
+
+namespace Drupal\Core\Ajax;
+
+use Drupal\Core\Ajax\SetDialogOptionCommand;
+
+/**
+ * Defines an AJAX command that sets jQuery UI dialog properties.
+ *
+ * @ingroup ajax
+ */
+class SetDialogTitleCommand extends SetDialogOptionCommand {
+
+  /**
+   * Constructs a SetDialogTitleCommand object.
+   *
+   * @param string $selector
+   *   The selector of the dialog whose title will be set. If set to an empty
+   *   value, the default modal dialog will be selected.
+   * @param string $title
+   *   The title that will be set on the dialog.
+   */
+  public function __construct($selector, $title) {
+    $this->selector = $selector ? $selector : '#drupal-modal';
+    $this->optionName = 'title';
+    $this->optionValue = $title;
+  }
+}

core/lib/Drupal/Core/Ajax/SettingsCommand.php

@@ -0,0 +1,71 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Ajax\SettingsCommand.
+ */
+
+namespace Drupal\Core\Ajax;
+
+use Drupal\Core\Ajax\CommandInterface;
+
+/**
+ * AJAX command for adjusting Drupal's JavaScript settings.
+ *
+ * The 'settings' command instructs the client either to use the given array as
+ * the settings for ajax-loaded content or to extend drupalSettings with the
+ * given array, depending on the value of the $merge parameter.
+ *
+ * This command is implemented by Drupal.AjaxCommands.prototype.settings()
+ * defined in misc/ajax.js.
+ *
+ * @ingroup ajax
+ */
+class SettingsCommand implements CommandInterface {
+
+  /**
+   * An array of key/value pairs of JavaScript settings.
+   *
+   * This will be used for all commands after this if they do not include their
+   * own settings array.
+   *
+   * @var array
+   */
+  protected $settings;
+
+  /**
+   * Whether the settings should be merged into the global drupalSettings.
+   *
+   * By default (FALSE), the settings that are passed to Drupal.attachBehaviors
+   * will not include the global drupalSettings.
+   *
+   * @var bool
+   */
+  protected $merge;
+
+  /**
+   * Constructs a SettingsCommand object.
+   *
+   * @param array $settings
+   *   An array of key/value pairs of JavaScript settings.
+   * @param bool $merge
+   *   Whether the settings should be merged into the global drupalSettings.
+   */
+  public function __construct(array $settings, $merge = FALSE) {
+    $this->settings = $settings;
+    $this->merge = $merge;
+  }
+
+  /**
+   * Implements Drupal\Core\Ajax\CommandInterface:render().
+   */
+  public function render() {
+
+    return array(
+      'command' => 'settings',
+      'settings' => $this->settings,
+      'merge' => $this->merge,
+    );
+  }
+
+}

core/lib/Drupal/Core/Ajax/UpdateBuildIdCommand.php

@@ -0,0 +1,65 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Ajax\UpdateBuildIdCommand.
+ */
+
+namespace Drupal\Core\Ajax;
+
+/**
+ * AJAX command for updating the value of a hidden form_build_id input element
+ * on a form. It requires the form passed in to have keys for both the old build
+ * ID in #build_id_old and the new build ID in #build_id.
+ *
+ * The primary use case for this Ajax command is to serve a new build ID to a
+ * form served from the cache to an anonymous user, preventing one anonymous
+ * user from accessing the form state of another anonymous user on Ajax enabled
+ * forms.
+ *
+ * This command is implemented by
+ * Drupal.AjaxCommands.prototype.update_build_id() defined in misc/ajax.js.
+ *O
+ * @ingroup ajax
+ */
+class UpdateBuildIdCommand implements CommandInterface {
+
+  /**
+   * Old build id.
+   *
+   * @var string
+   */
+  protected $old;
+
+  /**
+   * New build id.
+   *
+   * @var string
+   */
+  protected $new;
+
+  /**
+   * Constructs a UpdateBuildIdCommand object.
+   *
+   * @param string $old
+   *   The old build_id.
+   * @param string $new
+   *   The new build_id.
+   */
+  public function __construct($old, $new) {
+    $this->old = $old;
+    $this->new = $new;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function render() {
+    return [
+      'command' => 'update_build_id',
+      'old' => $this->old,
+      'new' => $this->new,
+    ];
+  }
+
+}