diff --git a/core/modules/system/tests/modules/js_ajax_test/js/js_ajax_test.ajax.es6.js b/core/modules/system/tests/modules/js_ajax_test/js/js_ajax_test.ajax.es6.js
index 116bad83f1..271b4e30b4 100644
--- a/core/modules/system/tests/modules/js_ajax_test/js/js_ajax_test.ajax.es6.js
+++ b/core/modules/system/tests/modules/js_ajax_test/js/js_ajax_test.ajax.es6.js
@@ -26,4 +26,24 @@
       `<div id="js_ajax_test_form_element">${JSON.stringify(data)}</div>`,
     );
   };
+
+  /**
+   * Test Ajax execution Order.
+   *
+   * @param {Drupal.Ajax} [ajax]
+   *   {@link Drupal.Ajax} object created by {@link Drupal.Ajax}.
+   * @param {object} response
+   *   The response from the Ajax request.
+   * @param {string} response.selector
+   *   A jQuery selector string.
+   */
+  Drupal.AjaxCommands.prototype.jsAjaxTestInsertPromise = function(ajax, response) {
+    const exec = $.Deferred();
+    setTimeout(() => {
+      this.insert(ajax, response);
+      exec.resolve();
+    }, Math.random() * 500);
+
+    return exec.promise();
+  };
 })(jQuery, Drupal);
diff --git a/core/modules/system/tests/modules/js_ajax_test/js/js_ajax_test.ajax.js b/core/modules/system/tests/modules/js_ajax_test/js/js_ajax_test.ajax.js
index 4d71a2f381..e85a19b153 100644
--- a/core/modules/system/tests/modules/js_ajax_test/js/js_ajax_test.ajax.js
+++ b/core/modules/system/tests/modules/js_ajax_test/js/js_ajax_test.ajax.js
@@ -15,4 +15,16 @@
     };
     $domElement.html("<div id=\"js_ajax_test_form_element\">".concat(JSON.stringify(data), "</div>"));
   };
+
+  Drupal.AjaxCommands.prototype.jsAjaxTestInsertPromise = function (ajax, response) {
+    var _this = this;
+
+    var exec = $.Deferred();
+    setTimeout(function () {
+      _this.insert(ajax, response);
+
+      exec.resolve();
+    }, Math.random() * 500);
+    return exec.promise();
+  };
 })(jQuery, Drupal);
\ No newline at end of file
diff --git a/core/modules/system/tests/modules/js_ajax_test/src/Ajax/JsAjaxTestCommandInsertPromise.php b/core/modules/system/tests/modules/js_ajax_test/src/Ajax/JsAjaxTestCommandInsertPromise.php
new file mode 100644
index 0000000000..ce63306c24
--- /dev/null
+++ b/core/modules/system/tests/modules/js_ajax_test/src/Ajax/JsAjaxTestCommandInsertPromise.php
@@ -0,0 +1,27 @@
+<?php
+
+namespace Drupal\js_ajax_test\Ajax;
+
+use Drupal\Core\Ajax\AppendCommand;
+use Drupal\Core\Ajax\CommandInterface;
+
+/**
+ * Test Ajax command.
+ */
+class JsAjaxTestCommandInsertPromise extends AppendCommand {
+
+  /**
+   * Implements Drupal\Core\Ajax\CommandInterface:render().
+   */
+  public function render() {
+
+    return [
+      'command' => 'jsAjaxTestInsertPromise',
+      'method' => 'append',
+      'selector' => $this->selector,
+      'data' => $this->getRenderedContent(),
+      'settings' => $this->settings,
+    ];
+  }
+
+}
diff --git a/core/modules/system/tests/modules/js_ajax_test/src/Form/JsAjaxTestForm.php b/core/modules/system/tests/modules/js_ajax_test/src/Form/JsAjaxTestForm.php
index 567d4158d6..735d57fbd1 100644
--- a/core/modules/system/tests/modules/js_ajax_test/src/Form/JsAjaxTestForm.php
+++ b/core/modules/system/tests/modules/js_ajax_test/src/Form/JsAjaxTestForm.php
@@ -3,9 +3,11 @@
 namespace Drupal\js_ajax_test\Form;
 
 use Drupal\Core\Ajax\AjaxResponse;
+use Drupal\Core\Ajax\AppendCommand;
 use Drupal\Core\Form\FormBase;
 use Drupal\Core\Form\FormStateInterface;
 use Drupal\js_ajax_test\Ajax\JsAjaxTestCommand;
+use Drupal\js_ajax_test\Ajax\JsAjaxTestCommandInsertPromise;
 
 /**
  * Test form for js_ajax_test
@@ -43,6 +45,21 @@ public function buildForm(array $form, FormStateInterface $form_state) {
         'wrapper' => 'js_ajax_test_form_wrapper',
       ],
     ];
+
+    // Button to test for the waitForButton() assertion.
+    $form['test_execution_order_button'] = [
+      '#type' => 'submit',
+      '#value' => $this->t('Execute commands button'),
+      '#button_type' => 'primary',
+      '#ajax' => [
+        'callback' => [static::class, 'executeCommands'],
+        'progress' => [
+          'type' => 'throbber',
+          'message' => NULL,
+        ],
+        'wrapper' => 'js_ajax_test_form_wrapper',
+      ],
+    ];
     return $form;
   }
 
@@ -54,6 +71,22 @@ public static function addButton(array $form, FormStateInterface $form_state) {
       ->addCommand(new JsAjaxTestCommand());
   }
 
+  /**
+   * Ajax callback for the "Execute commands button" button.
+   */
+  public static function executeCommands(array $form, FormStateInterface $form_state) {
+    $selector = '#js_ajax_test_form_wrapper';
+    $response = new AjaxResponse();
+
+    $response->addCommand(new AppendCommand($selector, '1'));
+    $response->addCommand(new JsAjaxTestCommandInsertPromise($selector, '2'));
+    $response->addCommand(new AppendCommand($selector, '3'));
+    $response->addCommand(new AppendCommand($selector, '4'));
+    $response->addCommand(new JsAjaxTestCommandInsertPromise($selector, '5'));
+
+    return $response;
+  }
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/tests/Drupal/Nightwatch/Tests/ajaxExecutionOrderTest.js b/core/tests/Drupal/Nightwatch/Tests/ajaxExecutionOrderTest.js
new file mode 100644
index 0000000000..3efbf3935c
--- /dev/null
+++ b/core/tests/Drupal/Nightwatch/Tests/ajaxExecutionOrderTest.js
@@ -0,0 +1,31 @@
+module.exports = {
+  '@tags': ['core', 'ajax'],
+  before(browser) {
+    browser.drupalInstall().drupalLoginAsAdmin(() => {
+      browser
+        .drupalRelativeURL('/admin/modules')
+        .setValue('input[type="search"]', 'JS Ajax test')
+        .waitForElementVisible(
+          'input[name="modules[js_ajax_test][enable]"]',
+          1000,
+        )
+        .click('input[name="modules[js_ajax_test][enable]"]')
+        .click('input[type="submit"]'); // Submit module form.
+    });
+  },
+  after(browser) {
+    browser.drupalUninstall();
+  },
+  'Test Execution Order': browser => {
+    browser
+      .drupalRelativeURL('/js_ajax_test')
+      .waitForElementVisible('body', 1000)
+      .click('[data-drupal-selector="edit-test-execution-order-button"]')
+      .waitForElementVisible('body', 1000)
+      .assert.containsText(
+        '#js_ajax_test_form_wrapper',
+        '12345',
+        'Execution order confirmed',
+      );
+  },
+};