Step 9 Adding Ajax
In this step we add Ajax to mod_hello and also describe
- how you can pass language strings down to javascript code, and,
- how you can display system messages from javascript.
The source code is available at mod_hello step 9.
com_ajax
Joomla provides a component com_ajax which allows a module's javascript code to make an Ajax call and get back an Ajax response.
In the javascript code we make an Ajax call to index.php?option=com_ajax&module=hello&method=count&format=json.
The URL parameters are interpreted as follows
- option=com_ajax means that Joomla will route this HTTP request to the com_ajax component. The rest of the URL parameters will be interpreted by com_ajax
- module=hello we want to route to the mod_hello module
- method=count com_ajax will call the countAjax() method of the module's helper class
- format=json we want the response in JSON format
How this works is shown by the sequence diagram
When com_ajax receives the result it uses the Joomla JsonResponse class to return the result to the javascript code.
mod_hello changes
To demonstrate the Ajax functionality we'll provide a button on the module which when clicked will trigger an Ajax request to obtain the number of logged-on users. The Ajax response will be:
- the number of logged-on users if the current user is logged-on
- a "not authorised" error if the current user isn't logged on
Our code changes in mod_hello are:
- In the tmpl file output a button which the user can click
- Create the js for making the Ajax call and handling the response
- Create the
countAjaxfunction in the helper class
tmpl file changes
Here's the updated tmpl file:
<?php
defined('_JEXEC') or die;
use Joomla\CMS\Language\Text;
$document = $this->app->getDocument();
$wa = $document->getWebAssetManager();
$wa->getRegistry()->addExtensionRegistryFile('mod_hello');
$wa->useScript('mod_hello.add-suffix');
// Pass the suffix to add down to js
$document->addScriptOptions('vars', ['suffix' => '!']);
$h = $params->get('header', 'h4');
$greeting = "<{$h} class='mod_hello'>{$hello}</{$h}>";
Text::script('MOD_HELLO_AJAX_OK');
Text::script('JLIB_JS_AJAX_ERROR_OTHER');
?>
<?php echo $greeting; ?>
<div>
<p><?php echo Text::_('MOD_HELLO_NUSERS'); ?><span class="mod_hello_nusers"></span></p>
<button class="mod_hello_updateusers"><?php echo Text::_('MOD_HELLO_UPDATE_NUSERS'); ?></button>
</div>
Here we've used the Text::script function to pass language strings down to the javascript code.
Text::script('MOD_HELLO_AJAX_OK');
will pass the language string 'MOD_HELLO_AJAX_OK' to make it available to the js code.
We can then interpret this language string in javascript using:
Joomla.Text._('MOD_HELLO_AJAX_OK')
You can find Joomla.text in the core.js library in media/system/js/core.js.
The 'JLIB_JS_AJAX_ERROR_OTHER' language string is in the lib_joomla.ini language file, and this is always loaded by Joomla as part of its initialisation.
javascript changes
For convenience we'll just add our Ajax code into add-suffix.js. The additional lines are:
const countUsers = (event) => {
const nusers = event.target.parentElement.querySelector('span.mod_hello_nusers');
Joomla.request({
url: 'index.php?option=com_ajax&module=hello&method=count&format=json',
method: 'GET',
onSuccess(data) {
const response = JSON.parse(data);
if (response.success) {
nusers.innerText = response.data;
const confirmation = Joomla.Text._('MOD_HELLO_AJAX_OK').replace('%s', response.data);
Joomla.renderMessages({ 'info': [confirmation] });
} else {
const messages = { 'error': [response.message] };
Joomla.renderMessages(messages);
}
},
onError(xhr) {
Joomla.renderMessages(Joomla.ajaxErrorsMessages(xhr));
const response = JSON.parse(xhr.response);
Joomla.renderMessages({ 'error': [response.message] }, undefined, true);
}
});
};
document.querySelectorAll('.mod_hello_updateusers').forEach(element => {
element.addEventListener('click', countUsers);
});
We set an onclick listener on the Update button, which when clicked results in the Ajax call being triggered.
Joomla.request is in core.js and is described here. Of course you can use your own preferred way of initiating Ajax requests.
Joomla.renderMessages is in media/system/js/messages.js and is used to display messages in the system message area of the HTML document.
Check the messages.js code for details of how to use it.
Because our code now depends on "messages" as well as "core" we need to update the joomla.asset.json.
Also we should update our javascript version number as that will ensure that any add-suffix.js code cached by the browser gets flushed.
{
"$schema": "https://developer.joomla.org/schemas/json-schema/web_assets.json",
"name": "mod_hello",
"version": "1.0.0",
"description": "Joomla Module Tutorial",
"license": "GPL-2.0-or-later",
"assets": [
{
"name": "mod_hello.add-suffix",
"type": "script",
"uri": "mod_hello/add-suffix.js",
"dependencies": [
"jquery", "core", "messages"
],
"version": "1.1.0"
}
]
}
Helper file changes
When you logon to the administrator back-end Joomla displays a list of the logged-on users.
With a little investigation you can find that this is output by an administrator module administrator/modules/mod_logged and that it contains a method getList in its helper file which returns a list of the logged-on users.
One option would be to use this code directly by making a call to \Joomla\Module\Logged\Administrator\Helper\LoggedHelper::getList() however reusing Joomla code like this is rather risky, as it could change between releases. In particular, when the module is updated from the old style (Joomla 3) to including dependency injection, then the getList function changes from being a static function to an instance function.
For this reason it's more straightforward just to copy the approach and use a similar database query, and the new lines in our helper file are as follows
use Joomla\Database\DatabaseInterface;
use Joomla\CMS\Language\Text;
...
public function countAjax()
{
$user = Factory::getApplication()->getIdentity();
if ($user->id == 0) {
// not logged on
throw new \Exception(Text::_('JERROR_ALERTNOAUTHOR'));
}
$db = Factory::getContainer()->get(DatabaseInterface::class);
$query = $db->getQuery(true)
->select('COUNT(*)')
->from('#__session AS s')
->where('s.guest = 0');
$db->setQuery($query);
return (string) $db->loadResult();
}
Note that com_ajax uses $module->getHelper(...) on the module Extension class to find the Helper class (as is described in step 8).
So you have to set up the HelperFactory in the services/provider.php file, as we have done in the dependency injection step.
New Language Strings
; language strings used inside mod_hello
MOD_HELLO_NAME="Joomla Module Tutorial"
MOD_HELLO_DESCRIPTION="Source code for the Joomla module tutorial"
MOD_HELLO_GREETING="Hello "
MOD_HELLO_HEADER_LEVEL="Header level of greeting"
MOD_HELLO_HEADER_LEVEL_3="Header level 3"
MOD_HELLO_HEADER_LEVEL_4="Header level 4"
MOD_HELLO_HEADER_LEVEL_5="Header level 5"
MOD_HELLO_HEADER_LEVEL_6="Header level 6"
MOD_HELLO_NUSERS="Number of logged-on users: "
MOD_HELLO_UPDATE_NUSERS="Update"
MOD_HELLO_AJAX_OK="Ajax response: %s received ok"
Manifest File changes
<?xml version="1.0" encoding="utf-8"?>
<extension type="module" client="site" method="upgrade">
<name>MOD_HELLO_NAME</name>
<version>1.0.9</version>
<author>me</author>
<creationDate>today</creationDate>
<description>MOD_HELLO_DESCRIPTION</description>
<namespace path="src">My\Module\Hello</namespace>
<files>
<folder module="mod_hello">services</folder>
<folder>src</folder>
<folder>tmpl</folder>
<folder>language</folder>
</files>
<scriptfile>script.php</scriptfile>
<media destination="mod_hello" folder="media">
<filename>joomla.asset.json</filename>
<folder>js</folder>
</media>
<config>
<fields name="params">
<fieldset name="basic">
<field
name="header"
type="list"
label="MOD_HELLO_HEADER_LEVEL"
>
<option value="h3">MOD_HELLO_HEADER_LEVEL_3</option>
<option value="h4">MOD_HELLO_HEADER_LEVEL_4</option>
<option value="h5">MOD_HELLO_HEADER_LEVEL_5</option>
<option value="h6">MOD_HELLO_HEADER_LEVEL_6</option>
</field>
</fieldset>
</fields>
</config>
</extension>