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) {
  // if card is less than 2 characters or more than 3 characters it is invalid
  // and check if not a string

  if (typeof card !== "string") {
    throw new Error("Invalid card");
  }

  if (!(card.length === 2 || (card.length === 3 && card.startsWith("10")))) {
    throw new Error("Invalid card");
  }

  const validSuits = ["♠", "♥", "♦", "♣"];

  let firstChar, suit;

  if (card.startsWith("10")) {
    firstChar = "10";
    suit = card[2]; //if it starts with 10 the third character is the suit
  } else {
    firstChar = card[0]; //otherwise
    suit = card[1]; //the second character is the suit
  }
  if (!suit || !validSuits.includes(suit)) {
    throw new Error("Invalid suit");
  }

  // check if picture cards
  if (firstChar === "A") return 11; // if Ace return 11
  if (["J", "Q", "K"].includes(firstChar)) return 10; // if Jack, Queen or King return 10

  const num = Number(firstChar);
  if (!isNaN(num) && num >= 2 && num <= 10) return num; //checks number is between 2 and 10

  // for everything else that is invalid
  throw new Error("Invalid number");
}

// 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);
assertEquals(getCardValue("10♥"), 10);
assertEquals(getCardValue("J♥"), 10);
assertEquals(getCardValue("A♠"), 11);
assertEquals(getCardValue("Q♦"), 10);
assertEquals(getCardValue("K♦"), 10);

// Handling invalid cards
try {
  getCardValue("♠J");
  console.error("Test failed: invalid first character accepted");
} catch (e) {
  console.log("Test passed:  Invalid first character rejected");
}

try {
  getCardValue("invalid");
  console.error("Test failed: invalid card accepted");
} catch (e) {
  console.log("Test passed: Invalid card rejected");
}

try {
  console.log(getCardValue("2♥2"));
} catch (e) {
  console.log("Invalid numbers caught");
}

try {
  console.log(getCardValue("2♥♥"));
} catch (e) {
  console.log("Invalid suit caught");
}

console.log(getCardValue("A♠"));
console.log(getCardValue("A♠"));
console.log(getCardValue("A♠"));
console.log(getCardValue("A♠"));
console.log(getCardValue("Q♦"));
console.log(getCardValue("K♣"));
console.log(getCardValue("A♠"));