minor #9528 Replace jQuery example with plain JavaScript (msheakoski)

This PR was submitted for the master branch but it was squashed and merged into the 3.4 branch instead (closes #9528).

Discussion
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Replace jQuery example with plain JavaScript

The data attributes example relies unnecessarily on jQuery and is potentially more confusing because it masks how attributes actually work in JavaScript and it's another level of abstraction to deal with. It is a better idea to promote web standards here because people tend to copy what they see, so let's steer them in a future-friendly direction.

Commits
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0dfcbd8 Replace jQuery example with plain JavaScript

Author: javiereguiluz

frontend/encore/server-data.rst

@@ -16,13 +16,18 @@ Fetch this in JavaScript:
 
 .. code-block:: javascript
 
-    // jquery isn't required, but makes things simple
-    var $ = require('jquery');
-
-    $(document).ready(function() {
-        var isAuthenticated = $('.js-user-rating').data('is-authenticated');
+    document.addEventListener('DOMContentLoaded', function() {
+        var userRating = document.querySelector('.js-user-rating');
+        var isAuthenticated = userRating.dataset.isAuthenticated;
     });
 
+.. note::
+
+    When `accessing data attributes from JavaScript`_, the attribute names are
+    converted from dash-style to camelCase. For example, ``data-is-authenticated``
+    becomes ``isAuthenticated`` and ``data-number-of-reviews`` becomes
+    ``numberOfReviews``.
+
 There is no size limit for the value of the ``data-`` attributes, so you can
 store any content. In Twig, use the ``html_attr`` escaping strategy to avoid messing
 with HTML attributes. For example, if your ``User`` object has some ``getProfileData()``
@@ -33,3 +38,5 @@ method that returns an array, you could do the following:
     <div data-user-profile="{{ app.user ? app.user.profileData|json_encode|e('html_attr') : '' }}">
         <!-- ... -->
     </div>
+
+.. _`accessing data attributes from JavaScript`: https://developer.mozilla.org/en-US/docs/Learn/HTML/Howto/Use_data_attributes