function foo(o) {
    return delete o.f;
}

noInline(foo);

for (var i = 0; i < 10000; ++i) {
    var o = {f:42};
    var result = foo(o);
    if (result !== true)
        throw "Error: bad result: " + result;
    if ("f" in o)
        throw "Error: \"f\" still in ok";
}