.. include:: ../../Includes.txt

==================================================
Feature: #89244 - Broadcast Channels and Messaging
==================================================

See :issue:`89244`

Description
===========

It is now possible to send broadcast messages from anywhere in TYPO3 that are listened to via JavaScript.

.. warning::

   This API is considered internal and may change anytime until declared being stable.


Send a message
--------------

Any backend module may send a message using the :js:`TYPO3/CMS/Backend/BroadcastService` module.
The payload of such message is an object that consists at least of the following properties:

* :js:`componentName` - the name of the component that sends the message (e.g. extension name)
* :js:`eventName` - the event name used to identify the message

A message may contain any other property as necessary. The final event name to listen is a composition of "typo3", the
component name and the event name, e.g. `typo3:my_extension:my_event`.

.. attention::

   Since a polyfill is in place to add support for Microsoft Edge, the payload must contain JSON-serializable content
   only.


To send a message, the :js:`post()` method has to be used.

Example code:

.. code-block:: js

   require(['TYPO3/CMS/Backend/BroadcastService'], function (BroadcastService) {
     const payload = {
       componentName: 'my_extension',
       eventName: 'my_event',
       hello: 'world',
       foo: ['bar', 'baz']
     };

     BroadcastService.post(payload);
   });


Receive a message
-----------------

To receive and thus react on a message, an event handler needs to be registered that listens to the composed event
name (e.g. `typo3:my_component:my_event`) sent to :js:`document`.

The event itself contains a property called `detail` **excluding** the component name and event name.

Example code:

.. code-block:: js

   define([], function() {
      document.addEventListener('typo3:my_component:my_event', (e) => eventHandler(e.detail));

      function eventHandler(detail) {
        console.log(detail); // contains 'hello' and 'foo' as sent in the payload
      }
   });


Hook into :php:`$GLOBALS['TYPO3_CONF_VARS']['SC_OPTIONS']['typo3/backend.php']['constructPostProcess']` to load a custom
:php:`BackendController` hook that loads the event handler, e.g. via RequireJS.

Example code:

.. code-block:: php

   // ext_localconf.php
   $GLOBALS['TYPO3_CONF_VARS']['SC_OPTIONS']['typo3/backend.php']['constructPostProcess'][]
       = \Vendor\MyExtension\Hooks\BackendControllerHook::class . '->registerClientSideEventHandler';

   // Classes/Hooks/BackendControllerHook.php
   class BackendControllerHook
   {
       public function registerClientSideEventHandler(): void
       {
           $pageRenderer = \TYPO3\CMS\Core\Utility\GeneralUtility::makeInstance(\TYPO3\CMS\Core\Page\PageRenderer::class);
           $pageRenderer->loadRequireJsModule('TYPO3/CMS/MyExtension/EventHandler');
       }
    }

.. index:: Backend, JavaScript, ext:backend
