MDL-38555 Forms: Prevent multiple clicking of submit button

lib/form/amd/src/submit.js

@@ -0,0 +1,48 @@
+// This file is part of Moodle - http://moodle.org/
+//
+// Moodle is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// Moodle is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with Moodle.  If not, see <http://www.gnu.org/licenses/>.
+
+/**
+ * Submit button JavaScript. All submit buttons will be automatically disabled once the form is
+ * submitted, unless that submission results in an error/cancelling the submit.
+ *
+ * @module core_form/submit
+ * @package core_form
+ * @copyright 2019 The Open University
+ * @license http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ * @since 3.8
+ */
+
+/**
+ * Initialises submit buttons.
+ *
+ * @param {String} elementId Form element
+ */
+export const init = (elementId) => {
+    const button = document.getElementById(elementId);
+    button.form.addEventListener('submit', function() {
+        // Only disable it if the browser is really going to another page as a result of the
+        // submit.
+        const disableAction = function() {
+            button.disabled = true;
+        };
+        window.addEventListener('beforeunload', disableAction);
+        // If there is no beforeunload event as a result of this form submit, then the form
+        // submit must have been cancelled, so don't disable the button if the page is
+        // unloaded later.
+        setTimeout(function() {
+            window.removeEventListener('beforeunload', disableAction);
+        }, 0);
+    }, false);
+};