Ajax API

Overview for Drupal's Ajax API.

Overview of Ajax

Ajax is the process of dynamically updating parts of a page's HTML based on data from the server. When a specified event takes place, a PHP callback is triggered, which performs server-side logic and may return updated markup or JavaScript commands to run. After the return, the browser runs the JavaScript or updates the markup on the fly, with no full page refresh necessary.

Many different events can trigger Ajax responses, including:

• Clicking a button
• Pressing a key
• Moving the mouse

Ajax responses in forms

Forms that use the Drupal Form API (see the Form API topic for more information about forms) can trigger AJAX responses. Here is an outline of the steps:

• Add property '#ajax' to a form element in your form array, to trigger an Ajax response.
• Write an Ajax callback to process the input and respond.

See sections below for details on these two steps.

Adding Ajax triggers to a form

As an example of adding Ajax triggers to a form, consider editing a date format, where the user is provided with a sample of the generated date output as they type. To accomplish this, typing in the text field should trigger an Ajax response. This is done in the text field form array element in \Drupal\config_translation\FormElement\DateFormat::getFormElement():

'#ajax' => [
  'callback' => 'Drupal\config_translation\FormElement\DateFormat::ajaxSample',
  'event' => 'keyup',
  'progress' => [
    'type' => 'throbber',
    'message' => NULL,
  ],
],

As you can see from this example, the #ajax property for a form element is an array. Here are the details of its elements, all of which are optional:

• callback: The callback to invoke to handle the server side of the Ajax event. More information on callbacks is below in Setting up a callback to process Ajax.
• wrapper: The HTML 'id' attribute of the area where the content returned by the callback should be placed. Note that callbacks have a choice of returning content or JavaScript commands; 'wrapper' is used for content returns.
• method: The jQuery method for placing the new content (used with 'wrapper'). Valid options are 'replaceWith' (default), 'append', 'prepend', 'before', 'after', or 'html'. See http://api.jquery.com/category/manipulation/ for more information on these methods.
• effect: The jQuery effect to use when placing the new HTML (used with 'wrapper'). Valid options are 'none' (default), 'slide', or 'fade'.
• speed: The effect speed to use (used with 'effect' and 'wrapper'). Valid options are 'slow' (default), 'fast', or the number of milliseconds the effect should run.
• event: The JavaScript event to respond to. This is selected automatically for the type of form element; provide a value to override the default.
• prevent: A JavaScript event to prevent when the event is triggered. For example, if you use event 'mousedown' on a button, you might want to prevent 'click' events from also being triggered.
• progress: An array indicating how to show Ajax processing progress. Can contain one or more of these elements:
  • type: Type of indicator: 'throbber' (default) or 'bar'.
  • message: Translated message to display.
  • url: For a bar progress indicator, URL path for determining progress.
  • interval: For a bar progress indicator, how often to update it.
• url: A \Drupal\Core\Url to which to submit the Ajax request. If omitted, defaults to either the same URL as the form or link destination is for someone with JavaScript disabled, or a slightly modified version (e.g., with a query parameter added, removed, or changed) of that URL if necessary to support Drupal's content negotiation. It is recommended to omit this key and use Drupal's content negotiation rather than using substantially different URLs between Ajax and non-Ajax.

Setting up a callback to process Ajax

Once you have set up your form to trigger an Ajax response (see Adding Ajax triggers to a form above), you need to write some PHP code to process the response. If you use 'path' in your Ajax set-up, your route controller will be triggered with only the information you provide in the URL. If you use 'callback', your callback method is a function, which will receive the $form and $form_state from the triggering form. You can use $form_state to get information about the data the user has entered into the form. For instance, in the above example for the date format preview, \Drupal\config_translation\FormElement\DateFormat\ajaxSample() does this to get the format string entered by the user:

$format_value = \Drupal\Component\Utility\NestedArray::getValue($form_state->getValues(), $form_state->getTriggeringElement()['#array_parents']);

Once you have processed the input, you have your choice of returning HTML markup or a set of Ajax commands. If you choose to return HTML markup, you can return it as a string or a renderable array, and it will be placed in the defined 'wrapper' element (see documentation above in Adding Ajax triggers to a form). In addition, any messages returned by \Drupal\Core\Messenger\Messenger::all(), themed as in status-messages.html.twig, will be prepended.

To return commands, you need to set up an object of class \Drupal\Core\Ajax\AjaxResponse, and then use its addCommand() method to add individual commands to it. In the date format preview example, the format output is calculated, and then it is returned as replacement markup for a div like this:

$response = new AjaxResponse();
$response->addCommand(new ReplaceCommand('#edit-date-format-suffix', '<small id="edit-date-format-suffix">' . $format . '</small>'));
return $response;

The individual commands that you can return implement interface \Drupal\Core\Ajax\CommandInterface. Available commands provide the ability to pop up alerts, manipulate text and markup in various ways, redirect to a new URL, and the generic \Drupal\Core\Ajax\InvokeCommand, which invokes an arbitrary jQuery command.

As noted above, status messages are prepended automatically if you use the 'wrapper' method and return HTML markup. This is not the case if you return commands, but if you would like to show status messages, you can add

[
    '#type' => 'status_messages',
];

to a render array, use \Drupal::service('renderer')->render() to render it, and add a command to place the messages in an appropriate location.

Other methods for triggering Ajax

Here are some additional methods you can use to trigger Ajax responses in Drupal:

• Add class 'use-ajax' to a link. The link will be loaded using an Ajax call. When using this method, the href of the link can contain '/nojs/' as part of the path. When the Ajax JavaScript processes the page, it will convert this to '/ajax/'. The server is then able to easily tell if this request was made through an actual Ajax request or in a degraded state, and respond appropriately.
• Add class 'use-ajax-submit' to a submit button in a form. The form will then be submitted via Ajax to the path specified in the #action. Like the ajax-submit class on links, this path will have '/nojs/' replaced with '/ajax/' so that the submit handler can tell if the form was submitted in a degraded state or not.
• Add property '#autocomplete_route_name' to a text field in a form. The route controller for this route must return an array of options for autocomplete, as a \Symfony\Component\HttpFoundation\JsonResponse object. See the Routing topic for more information about routing.

Query parameters in Ajax requests

If a form uses an Ajax field, all the query parameters in the current request will be also added to the Ajax POST requests along with an additional 'ajax_form=1' parameter (See \Drupal\Core\Render\Element\RenderElementBase).

$settings['options']['query'] += \Drupal::request()->query
    ->all();
$settings['options']['query'][FormBuilderInterface::AJAX_FORM_REQUEST] = TRUE;

Form elements of type 'managed_file' will have an additional 'element_parents' query parameter in Ajax POST requests. This parameter will include the name of the element and its parents as per the render array. This helps to identify the position of the element in the form (See \Drupal\file\Element\ManagedFile).

'options' => [
  'query' => [
    'element_parents' => implode('/', $element['#array_parents']),
  ],
],

File

core/core.api.php, line 2375

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