--- /dev/null
+// WeakMap constructor with adder change.
+
+var originalAdder = WeakMap.prototype.set;
+var counter = 0;
+
+WeakMap.prototype.set = function (key, value) {
+ counter++;
+ return originalAdder.call(this, key, value);
+};
+
+var obj0 = {};
+var obj1 = {};
+var obj2 = [];
+var obj3 = new Date();
+var obj4 = new Error();
+var obj5 = JSON;
+
+var values = [
+ [ obj0, 0 ],
+ [ obj1, 1 ],
+ [ obj2, 2 ],
+ [ obj3, 3 ],
+ [ obj4, 4 ],
+ [ obj5, 5 ],
+ [ obj4, 4 ],
+ [ obj3, 3 ],
+ [ obj2, 2 ],
+ [ obj1, 1 ],
+ [ obj0, 0 ],
+];
+var map = new WeakMap(values);
+if (counter !== values.length)
+ throw "Error: bad counter " + counter;
+
+WeakMap.prototype.set = function () {
+ throw new Error("adder called");
+};
+
+var map = new WeakMap();
+var map = new WeakMap([]);
+var error = null;
+try {
+ var map = new WeakMap([ [0, 0] ]);
+} catch (e) {
+ error = e;
+}
+if (!error)
+ throw "Error: error not thrown";
+if (String(error) !== "Error: adder called")
+ throw "Error: bad error " + String(error);
+