1 files changed, 46 insertions, 0 deletions
diff --git a/ext/bg/js/settings.js b/ext/bg/js/settings.js
index e4446851..d4b1549e 100644
--- a/ext/bg/js/settings.js
+++ b/ext/bg/js/settings.js
@@ -212,6 +212,52 @@ $(document).ready(utilAsync(onReady));
 
 
 /*
+ * Page exit prevention
+ */
+
+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();
+
+
+/*
  * Appearance
  */