var sym = Symbol('foo');

​

var args = {

    [sym]: 1,

    bar() {}

};

​

function foo(obj) {

    var arr = [];

    for (var key in obj) {

        arr.push(key);

        arr.push(obj[key]);

    }

    return arr;

}

console.log(foo(args));

​

var c = 3000;

while (c--) {

    foo({c: c});

}

console.log(foo(args));

​

​

​