null.js

let cards = {
  Q: { colorCards: "lol", equity: 42 },
  A: { colorCards: "lol", equity: 42 }
};

let defaultHand = {
  colorCards: "AAA",
  equity: 40
};

function getHand(cards, hand) {
  return Object.assign(cards, {
    get [hand]() {
      return cards[hand] || defaultHand;
    }
  })[hand];
}

console.log(getHand(cards, "Q"));
console.log(getHand(cards, "A"));
console.log(getHand(cards, "J"));
console.log(getHand(cards, "K"));

console.log(getHand(cards, "Q").colorCards);
console.log(getHand(cards, "A").colorCards);
console.log(getHand(cards, "J").colorCards);
console.log(getHand(cards, "K").colorCards);

// { colorCards: 'lol', equity: 42 }
// { colorCards: 'lol', equity: 42 }
// { colorCards: 'AAA', equity: 40 }
// { colorCards: 'AAA', equity: 40 }
// lol
// lol
// AAA
// AAA