// The argument to WeakMap can be a generator. var k1 = {}; var v1 = 42; var k2 = {}; var v2 = 43; var k3 = {}; var done = false; function* data() { yield [k1, v1]; yield [k2, v2]; done = true; }; m = new WeakMap(data()); assertEq(done, true); // the constructor consumes the argument assertEq(m.has(k1), true); assertEq(m.has(k2), true); assertEq(m.has(k3), false); assertEq(m.get(k1), v1); assertEq(m.get(k2), v2); assertEq(m.get(k3), undefined);