1 files changed, 33 insertions, 0 deletions
diff --git a/testing/web-platform/tests/html/browsers/browsing-the-web/unloading-documents/beforeunload-synchronous.html b/testing/web-platform/tests/html/browsers/browsing-the-web/unloading-documents/beforeunload-synchronous.html
new file mode 100644
index 0000000000..6806eaf7a3
--- /dev/null
+++ b/testing/web-platform/tests/html/browsers/browsing-the-web/unloading-documents/beforeunload-synchronous.html
@@ -0,0 +1,33 @@
+<!DOCTYPE html>
+<meta charset="utf-8">
+<title>beforeunload event is emitted synchronously</title>
+<link rel="help" href="https://html.spec.whatwg.org/multipage/webappapis.html#the-event-handler-processing-algorithm">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<body>
+<script>
+'use strict';
+// "navigate a browsing context" synchronously calls "prompt to unload", which
+// synchronously calls "dispatch an event".
+
+async_test(function(t) {
+  var iframe = document.createElement('iframe');
+
+  iframe.onload = t.step_func(function() {
+    var callCount = 0;
+
+    iframe.contentWindow.onbeforeunload = function() {
+      callCount += 1;
+    };
+
+    iframe.contentWindow.location.href = '/common/blank.html';
+
+    assert_equals(callCount, 1, 'invoked synchronously exactly once');
+
+    t.done();
+  });
+
+  document.body.appendChild(iframe);
+});
+</script>
+</body>