Little cli game to learn the greek alphabet

index.js

const readline = require("readline");

const greekAlphabet = {
  Α: "Alpha",
  Β: "Beta",
  Γ: "Gamma",
  Δ: "Delta",
  Ε: "Epsilon",
  Ζ: "Zeta",
  Η: "Eta",
  Θ: "Theta",
  Ι: "Iota",
  Κ: "Kappa",
  Λ: "Lambda",
  Μ: "Mu",
  Ν: "Nu",
  Ξ: "Xi",
  Ο: "Omicron",
  Π: "Pi",
  Ρ: "Rho",
  Σ: "Sigma",
  Τ: "Tau",
  Υ: "Upsilon",
  Φ: "Phi",
  Χ: "Chi",
  Ψ: "Psi",
  Ω: "Omega",
  α: "Alpha",
  β: "Beta",
  γ: "Gamma",
  δ: "Delta",
  ε: "Epsilon",
  ζ: "Zeta",
  η: "Eta",
  θ: "Theta",
  ι: "Iota",
  κ: "Kappa",
  λ: "Lambda",
  μ: "Mu",
  ν: "Nu",
  ξ: "Xi",
  ο: "Omicron",
  π: "Pi",
  ρ: "Rho",
  σ: "Sigma",
  τ: "Tau",
  υ: "Upsilon",
  φ: "Phi",
  χ: "Chi",
  ψ: "Psi",
  ω: "Omega",
};

const letterAmount = Object.keys(greekAlphabet).length;
let mistakes = 0;

const rl = readline.createInterface({
  input: process.stdin,
  output: process.stdout,
});

function getRandomLetter() {
  const keys = Object.keys(greekAlphabet);
  if (keys.length === 0) {
    return null;
  }
  const randomIndex = Math.floor(Math.random() * keys.length);
  return keys[randomIndex];
}

function askQuestion() {
  const randomLetter = getRandomLetter();

  if (randomLetter) {
    const correctAnswer = greekAlphabet[randomLetter];

    rl.question(
      `${randomLetter} (${
        Object.keys(greekAlphabet).length
      }/${letterAmount}): `,
      (answer) => {
        if (answer.toLowerCase() === correctAnswer.toLowerCase()) {
          console.log("Correct! Well done.\n");

          // Mark the question as asked
          delete greekAlphabet[randomLetter];
        } else {
          console.log(`Incorrect. The correct answer is ${correctAnswer}.\n`);
          mistakes++;
        }

        askQuestion();
      },
    );
  } else {
    console.log("Congratulations! You've answered all the questions.\n");
    console.log(`You made ${mistakes} mistake(s).`);
    rl.close();
  }
}

console.log("Let's quiz on the Greek alphabet!\n");

askQuestion();