// don't assert var f = function(){}; for (var p in f); Object.defineProperty(f, "j", ({configurable: true, value: "a"})); Object.defineProperty(f, "k", ({configurable: true, value: "b"})); Object.defineProperty(f, "j", ({configurable: true, get: function() {}})); delete f.k; Object.defineProperty(f, "j", ({configurable: false}));