[Nexus]

var cards = [];
cards[123] = {
    balance: 3500,
    limit: 7000
};
cards[241] = {
    balance: 8000,
    limit: 10000
};

var forValueContainer=cards.slice();

console.log(
    forValueContainer.sort((a, b) => a.limit - b.limit).shift(), //object
    Object.keys(cards).sort((a, b) => cards[a].limit - cards[b].limit).shift() //key
);