MDL-67513 forum: View conversations while fullscreen grading

Before this change when a modal was shown and an element on the page
was fullscreen the modal would be created behind it.

This change ensures that the modal will be inside an element that is
fullscreen so that it will be correctly displayed.

lib/amd/src/fullscreen.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/>.
+
+/**
+ * Detects if an element is fullscreen.
+ *
+ * @module     core/fullscreen
+ * @class      fullscreen
+ * @package    core
+ * @copyright  2020 University of Nottingham
+ * @author     Neill Magill <[email protected]>
+ * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ */
+
+/**
+ * Gets the element that is fullscreen or null if no element is fullscreen.
+ *
+ * @returns {HTMLElement}
+ */
+export const getElement = () => {
+    let element = null;
+    if (document.fullscreenElement) {
+        element = document.fullscreenElement;
+    } else if (document.mozFullscreenElement) {
+        // Fallback for older Firefox.
+        element = document.mozFullscreenElement;
+    } else if (document.msFullscreenElement) {
+        // Fallback for Edge and IE.
+        element = document.msFullscreenElement;
+    } else if (document.webkitFullscreenElement) {
+        // Fallback for Chrome, Edge and Safari.
+        element = document.webkitFullscreenElement;
+    }
+
+    return element;
+};