1 files changed, 79 insertions, 0 deletions
diff --git a/js/xpconnect/tests/unit/test_classesByID_instanceof.js b/js/xpconnect/tests/unit/test_classesByID_instanceof.js
new file mode 100644
index 000000000..b0acf8016
--- /dev/null
+++ b/js/xpconnect/tests/unit/test_classesByID_instanceof.js
@@ -0,0 +1,79 @@
+function testActual(SimpleURIClassByID)
+{
+  var simpleURI =
+    Components.classes["@mozilla.org/network/simple-uri;1"].createInstance();
+
+  do_check_eq(simpleURI instanceof SimpleURIClassByID, true);
+}
+
+function testInherited(SimpleURIClassByID)
+{
+  var simpleURI =
+    Components.classes["@mozilla.org/network/simple-uri;1"].createInstance();
+
+  var inherited = Object.create(simpleURI);
+
+  do_check_eq(inherited instanceof SimpleURIClassByID, true);
+}
+
+function testInheritedCrossGlobal(SimpleURIClassByID)
+{
+  var simpleURI =
+    Components.classes["@mozilla.org/network/simple-uri;1"].createInstance();
+
+  var sb = new Components.utils.Sandbox(this, { wantComponents: true });
+  var inheritedCross = sb.Object.create(simpleURI);
+
+  do_check_eq(inheritedCross instanceof SimpleURIClassByID, true);
+}
+
+function testCrossGlobalArbitraryGetPrototype(SimpleURIClassByID)
+{
+  var simpleURI =
+    Components.classes["@mozilla.org/network/simple-uri;1"].createInstance();
+
+  var sb = new Components.utils.Sandbox(this, { wantComponents: true });
+  var firstLevel = Object.create(simpleURI);
+
+  var obj = { shouldThrow: false };
+  var secondLevel =
+    new sb.Proxy(Object.create(firstLevel),
+                 {
+                   getPrototypeOf: new sb.Function("obj", `return function(t) {
+                     if (obj.shouldThrow)
+                       throw 42;
+                     return Reflect.getPrototypeOf(t);
+                   };`)(obj)
+                 });
+  var thirdLevel = Object.create(secondLevel);
+
+  obj.shouldThrow = true;
+
+  var threw = false;
+  var err;
+  try
+  {
+    void (thirdLevel instanceof SimpleURIClassByID);
+  }
+  catch (e)
+  {
+    threw = true;
+    err = e;
+  }
+
+  do_check_eq(threw, true);
+  do_check_eq(err, 42);
+
+  obj.shouldThrow = false;
+
+  do_check_eq(thirdLevel instanceof SimpleURIClassByID, true);
+}
+
+function run_test() {
+  var SimpleURIClassByID = Components.classesByID["{e0da1d70-2f7b-11d3-8cd0-0060b0fc14a3}"];
+
+  testActual(SimpleURIClassByID);
+  testInherited(SimpleURIClassByID);
+  testInheritedCrossGlobal(SimpleURIClassByID);
+  testCrossGlobalArbitraryGetPrototype(SimpleURIClassByID);
+}