1 files changed, 42 insertions, 0 deletions
diff --git a/js/src/tests/non262/PrivateName/modify-non-extensible.js b/js/src/tests/non262/PrivateName/modify-non-extensible.js
new file mode 100644
index 0000000000..b57f82b38e
--- /dev/null
+++ b/js/src/tests/non262/PrivateName/modify-non-extensible.js
@@ -0,0 +1,42 @@
+// |reftest| shell-option(--enable-private-fields) skip-if(!xulRuntime.shell) -- requires shell-options
+
+// Returns the argument in the constructor to allow stamping private fields into
+// arbitrary objects.
+class OverrideBase {
+  constructor(o) {
+    return o;
+  }
+};
+
+class A extends OverrideBase {
+  #a = 1;
+  g() {
+    return this.#a
+  }
+
+  static gs(o) {
+    return o.#a;
+  }
+  static inca(obj) {
+    obj.#a++;
+  }
+}
+
+var obj = {};
+Object.seal(obj);
+new A(obj);  // Add #a to obj, but not g.
+assertEq('g' in obj, false);
+assertEq(A.gs(obj), 1);
+A.inca(obj);
+assertEq(A.gs(obj), 2);
+
+// Ensure that the object remains non-extensible
+obj.h = 'hi'
+assertEq('h' in obj, false);
+
+
+Object.freeze(obj);
+A.inca(obj);  // Despite being frozen, private names are modifiable.
+assertEq(A.gs(obj), 3);
+
+if (typeof reportCompare === 'function') reportCompare(0, 0);