minor #16157 [Form] Ajax success method is never call (Yoann-TYT)

This PR was merged into the 5.3 branch.

Discussion
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[Form] Ajax success method is never call

The method `renderForm` generate a `422 Unprocessable Entity` if the form is invalid. So we can’t pass in the `success` method. I suggest to replace it with the `complete` method.

Commits
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8a5ac31 The method renderForm generate a 422 Unprocessable Entity if the form is invalid. So we can’t pass in the success method. I suggest to replace it with the complete method.

Author: javiereguiluz

form/dynamic_form_modification.rst

@@ -568,11 +568,11 @@ field according to the current selection in the ``sport`` field:
         url : $form.attr('action'),
         type: $form.attr('method'),
         data : data,
-        success: function(html) {
+        complete: function(html) {
           // Replace current position field ...
           $('#meetup_position').replaceWith(
             // ... with the returned one from the AJAX response.
-            $(html).find('#meetup_position')
+            $(html.responseText).find('#meetup_position')
           );
           // Position field now displays the appropriate positions.
         }