3-get-card-value.js

// This problem involves playing cards: https://en.wikipedia.org/wiki/Standard_52-card_deck

// Implement a function getCardValue, when given a string representing a playing card,
// should return the numerical value of the card.

// A valid card string will contain a rank followed by the suit.
// The rank can be one of the following strings:
//   "A", "2", "3", "4", "5", "6", "7", "8", "9", "10", "J", "Q", "K"
// The suit can be one of the following emojis:
//   "♠", "♥", "♦", "♣"
// For example: "A♠", "2♥", "10♥", "J♣", "Q♦", "K♦".

// When the card is an ace ("A"), the function should return 11.
// When the card is a face card ("J", "Q", "K"), the function should return 10.
// When the card is a number card ("2" to "10"), the function should return its numeric value.

// When the card string is invalid (not following the above format), the function should
// throw an error.

// Acceptance criteria:
// After you have implemented the function, write tests to cover all the cases, and
// execute the code to ensure all tests pass.

function getCardValue(card) {
  const rank = card.slice(0, -1);
  const lastChar = card.slice(-1);
  const validSuits = ["♠", "♥", "♦", "♣"];

  if (!validSuits.includes(lastChar)) {
    throw new Error("Invalid card suit");
  }

  if (rank === "A") return 11;
  if (rank === "10" || rank === "J" || rank === "Q" || rank === "K") return 10;

  const rankNum = Number(rank);
  if (
    !Number.isNaN(rankNum) &&
    Number.isInteger(rankNum) &&
    rankNum >= 2 &&
    rankNum < 10 &&
    rank === rankNum.toString()
  ) {
    return rankNum;
  }

  throw new Error("Invalid card rank");
}

// The line below allows us to load the getCardValue function into tests in other files.
// This will be useful in the "rewrite tests with jest" step.
module.exports = getCardValue;

// Helper functions to make our assertions easier to read.
function assertEquals(actualOutput, targetOutput) {
  console.assert(
    actualOutput === targetOutput,
    `Expected ${actualOutput} to equal ${targetOutput}`
  );
}

// TODO: Write tests to cover all outcomes, including throwing errors for invalid cards.
// Examples:
assertEquals(getCardValue("9♠"), 9);

// Handle Number Cards (2-10):
// Given a card with a rank between "2" and "9",
// When the function is called with such a card,
// Then it should return the numeric value corresponding to the rank (e.g., "5" should return 5).
const fiveofHearts = getCardValue("5♥");
// ====> write your test here, and then add a line to pass the test in the function above
assertEquals(fiveofHearts, 5);

// Handle Face Cards (J, Q, K):
// Given a card with a rank of "10," "J," "Q," or "K",
// When the function is called with such a card,
// Then it should return the value 10, as these cards are worth 10 points each in blackjack.
const kingofDiamonds = getCardValue("K♦");
assertEquals(kingofDiamonds, 10);

// Handle Ace (A):
// Given a card with a rank of "A",
// When the function is called with an Ace,
// Then it should, by default, assume the Ace is worth 11 points, which is a common rule in blackjack.
const aceofClubs = getCardValue("A♣");
assertEquals(aceofClubs, 11);

// Handle Invalid Cards:
// Given a card with an invalid rank (neither a number nor a recognized face card),
// When the function is called with such a card,
// Then it should throw an error indicating "Invalid card rank."
try {
  getCardValue("1♠");
} catch (error) {
  assertEquals(error.message, "Invalid card rank");
}