Javascript (ES6) Immutable Data Example

// cardInfo has all the information of each card that never has to change, e.g. card name, stats etc.
const cardInfo = {
  1: {
    name: "Card 1",
    info: "This is card 1"
  },
  2: {
    name: "Card 2",
    info: "This is card 2"
  },
  3: {
    name: "Card 3",
    info: "This is card 3"
  },
  4: {
    name: "Card 4",
    info: "This is card 4"
  }
};

const initDecklist = new Map();
initDecklist.set(1,{quantity: 1});
initDecklist.set(3,{quantity: 2});

let state = {
  decklist: initDecklist
};

const exampleCardToAdd = {
  id: 1
};

const exampleCardToAddAgain = {
  id: 4
};

const setState = (newState = {}) => {
  try {
    state = Object.assign(state, newState)
  } catch (e) {
    console.error(`Unable to update state with ${newState}`);
  }
}

const addCard = (cardId, oldDecklist, quantity = 1) => {
  const newDecklist = new Map(oldDecklist);
  if (newDecklist.has(cardId)) {
    const oldObject = newDecklist.get(cardId)
    const newObject = Object.assign(
      {},
      oldObject,
      {
        quantity: oldObject.quantity + quantity
      }
    );
    newDecklist.set(cardId, newObject);
  } else {
    newDecklist.set(cardId, { quantity });
  }
  return newDecklist;
}

const addCardToDeck = cardToAdd => {
  const { decklist } = state;
  const newDecklist = addCard(cardToAdd.id, decklist);
  setState({ decklist: newDecklist});
}

const addCardToDeckTwice = cardToAdd => {
  const { decklist } = state;
  const newDecklist = addCard(cardToAdd.id, decklist, 2);
  setState({ decklist: newDecklist});
}

const printCards = () => {
  const { decklist } = state;
  for (let [id, v] of decklist.entries()) {
    const details = cardInfo[id];
    console.log(`+++\nCard: ${details.name}\nQuantity: ${v.quantity}\nInfo: ${details.info}`);
  }
}

console.log(state);
// { decklist: Map { 1 => { quantity: 1 }, 3 => { quantity: 2 } } }

addCardToDeck(exampleCardToAdd);

console.log(state);
// { decklist: Map { 1 => { quantity: 2 }, 3 => { quantity: 2 } } }

addCardToDeckTwice(exampleCardToAddAgain);

console.log(state);
/*
{ decklist:
   Map {
     1 => { quantity: 2 },
     3 => { quantity: 2 },
     4 => { quantity: 2 } } }
*/

printCards();
/*
+++
Card: Card 1
Quantity: 2
Info: This is card 1
+++
Card: Card 3
Quantity: 2
Info: This is card 3
+++
Card: Card 4
Quantity: 2
Info: This is card 4
*/