1 files changed, 23 insertions, 0 deletions
diff --git a/js/xpconnect/tests/unit/test_xpcwn_instanceof.js b/js/xpconnect/tests/unit/test_xpcwn_instanceof.js
new file mode 100644
index 0000000000..96268fd0b4
--- /dev/null
+++ b/js/xpconnect/tests/unit/test_xpcwn_instanceof.js
@@ -0,0 +1,23 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+// Tests for custom `instanceof` behavior via XPC_SCRIPTABLE_WANT_HASINSTANCE.
+
+add_task(function id_instanceof() {
+  // ID objects are instances of Components.ID.
+  let id = Components.ID("{f2f5c784-7f6c-43f5-81b0-45ff32c312b1}");
+  Assert.equal(id instanceof Components.ID, true);
+  Assert.equal({} instanceof Components.ID, false);
+  Assert.equal(null instanceof Components.ID, false);
+
+  // Components.ID has a Symbol.hasInstance function.
+  let desc = Object.getOwnPropertyDescriptor(Components.ID, Symbol.hasInstance);
+  Assert.equal(typeof desc, "object");
+  Assert.equal(typeof desc.value, "function");
+
+  // Test error handling when calling this function with unexpected values.
+  Assert.throws(() => desc.value.call(null), /At least 1 argument required/);
+  Assert.throws(() => desc.value.call(null, 1), /unexpected this value/);
+  Assert.throws(() => desc.value.call({}, {}), /NS_ERROR_XPC_BAD_OP_ON_WN_PROTO/);
+});