3 files changed, 40 insertions, 0 deletions
diff --git a/dom/base/CustomElementRegistry.cpp b/dom/base/CustomElementRegistry.cpp
index 761a791130..c52d2cc986 100644
--- a/dom/base/CustomElementRegistry.cpp
+++ b/dom/base/CustomElementRegistry.cpp
@@ -77,6 +77,7 @@ CustomElementConstructor::Construct(const char* aExecutionReason,
   JS::Rooted<JSObject*> result(cx);
   JS::Rooted<JS::Value> constructor(cx, JS::ObjectValue(*mCallback));
   if (!JS::Construct(cx, constructor, JS::HandleValueArray::empty(), &result)) {
+    aRv.NoteJSContextException(cx);
     return nullptr;
   }
 
diff --git a/dom/tests/mochitest/webcomponents/mochitest.ini b/dom/tests/mochitest/webcomponents/mochitest.ini
index 3559f33c19..f5d0f84ea9 100644
--- a/dom/tests/mochitest/webcomponents/mochitest.ini
+++ b/dom/tests/mochitest/webcomponents/mochitest.ini
@@ -21,6 +21,8 @@ skip-if = true || stylo # disabled - See bug 1390396 and 1293844
 [test_custom_element_throw_on_dynamic_markup_insertion.html]
 [test_custom_element_get.html]
 [test_custom_element_when_defined.html]
+[test_custom_element_uncatchable_exception.html]
+skip-if = !debug # TestFunctions only applied in debug builds
 [test_nested_content_element.html]
 [test_dest_insertion_points.html]
 [test_dest_insertion_points_shadow.html]
diff --git a/dom/tests/mochitest/webcomponents/test_custom_element_uncatchable_exception.html b/dom/tests/mochitest/webcomponents/test_custom_element_uncatchable_exception.html
new file mode 100644
index 0000000000..f60bf16742
--- /dev/null
+++ b/dom/tests/mochitest/webcomponents/test_custom_element_uncatchable_exception.html
@@ -0,0 +1,37 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=1407669
+-->
+<head>
+  <title>Test custom elements runtime exception</title>
+  <script type="text/javascript" src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1407669">Bug 1407669</a>
+<script type="text/javascript">
+
+SimpleTest.waitForExplicitFinish();
+SpecialPowers.pushPrefEnv({set: [['dom.expose_test_interfaces', true]]}, function() {
+  window.onerror = function (e) {
+    ok(false, "How did we get here!?");
+  }
+
+  class Foo extends HTMLElement {
+    constructor() {
+      super()
+      TestFunctions.throwUncatchableException();
+    }
+  }
+
+  customElements.define("test-custom-element", Foo);
+  let element = document.createElement("test-custom-element");
+  is(element instanceof HTMLUnknownElement, true, "It should be a HTMLUnknownElement when uncatchable exception throws in constructor");
+  ok(true, "Uncatchable exception should not report");
+  SimpleTest.finish();
+});
+
+</script>
+</body>
+</html>