1 files changed, 60 insertions, 0 deletions
diff --git a/ext/bg/js/page-exit-prevention.js b/ext/bg/js/page-exit-prevention.js
new file mode 100644
index 00000000..aee4e3c2
--- /dev/null
+++ b/ext/bg/js/page-exit-prevention.js
@@ -0,0 +1,60 @@
+/*
+ * Copyright (C) 2019  Alex Yatskov <alex@foosoft.net>
+ * Author: Alex Yatskov <alex@foosoft.net>
+ *
+ * This program 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.
+ *
+ * This program 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 this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+
+class PageExitPrevention {
+  constructor() {
+  }
+
+  start() {
+      PageExitPrevention._addInstance(this);
+  }
+
+  end() {
+      PageExitPrevention._removeInstance(this);
+  }
+
+  static _addInstance(instance) {
+      const size = PageExitPrevention._instances.size;
+      PageExitPrevention._instances.set(instance, true);
+      if (size === 0) {
+          window.addEventListener('beforeunload', PageExitPrevention._onBeforeUnload);
+      }
+  }
+
+  static _removeInstance(instance) {
+      if (
+          PageExitPrevention._instances.delete(instance) &&
+          PageExitPrevention._instances.size === 0
+      ) {
+          window.removeEventListener('beforeunload', PageExitPrevention._onBeforeUnload);
+      }
+  }
+
+  static _onBeforeUnload(e) {
+      if (PageExitPrevention._instances.size === 0) {
+          return;
+      }
+
+      e.preventDefault();
+      e.returnValue = '';
+      return '';
+  }
+}
+
+PageExitPrevention._instances = new Map();