TypeScript Project: Quiz Game

What you will build

A quiz is a list of prompts and the string that counts as correct. You print a question, compare a given answer, add one to the score on a match, then print a short report. The list is a Question[]. The given answers in this tutorial are a fixed sequence so the output is the same every run.

That fixed sequence is the point of the demo: you can read the tally and know which items were right. ClickTry it in TypeScript to compile at /typescript/try. Do not paste this into Python or C++.

A Question interface

Each item needs a prompt and an answer. Keep both as string so a correct reply can be a word, not only a letter. One object is one question. The quiz will hold several.

interface Question {
  prompt: string;
  answer: string;
}

const q: Question = {
  prompt: "How many bits in a byte?",
  answer: "8",
};

console.log(q.prompt);
console.log("Answer: " + q.answer);

Store the quiz in an array

Push each question onto an array. A loop can then print every prompt. The length of the quiz islength, so adding a question does not require a new array bound.

interface Question {
  prompt: string;
  answer: string;
}

const quiz: Question[] = [];
quiz.push({ prompt: "How many bits in a byte?", answer: "8" });
quiz.push({ prompt: "TypeScript compiler command?", answer: "tsc" });
quiz.push({ prompt: "Keyword for a class field that callers cannot touch?", answer: "private" });

for (let i = 0; i < quiz.length; i++) {
  console.log(i + 1 + ". " + quiz[i].prompt);
}

Check one answer

Compare the given string to question.answer. Exact match scores a point. This demo keeps comparisons case-sensitive so you see when a reply is almost right but not counted. A helper returns 1 or 0 so the tally is a running sum.

interface Question {
  prompt: string;
  answer: string;
}

function mark(q: Question, given: string): number {
  if (given === q.answer) {
    console.log("Correct");
    return 1;
  }
  console.log("Wrong (expected " + q.answer + ")");
  return 0;
}

const q: Question = { prompt: "Capital of France?", answer: "Paris" };
console.log(q.prompt);
let score = 0;
score = score + mark(q, "Paris");
score = score + mark(q, "paris");
console.log("Score " + score);

First given answer matches. Second does not, because P and p differ. Score is 1.

Complete quiz with a fixed sequence

Pair each question with a given reply in a second array of the same length. Walk both with one index. Never callreadLine() here: the sequence is part of the program so the report is deterministic. A later version can fill given from the keyboard.

interface Question {
  prompt: string;
  answer: string;
}

function mark(q: Question, given: string): number {
  console.log("You: " + given);
  if (given === q.answer) {
    console.log("Correct");
    return 1;
  }
  console.log("Wrong (expected " + q.answer + ")");
  return 0;
}

const quiz: Question[] = [];
quiz.push({ prompt: "How many bits in a byte?", answer: "8" });
quiz.push({ prompt: "TypeScript compiler command?", answer: "tsc" });
quiz.push({ prompt: "Keyword for a class field that callers cannot touch?", answer: "private" });
quiz.push({ prompt: "2 + 2?", answer: "4" });

const given: string[] = [];
given.push("8");
given.push("node");
given.push("private");
given.push("4");

let score = 0;
for (let i = 0; i < quiz.length; i++) {
  console.log(i + 1 + ". " + quiz[i].prompt);
  score = score + mark(quiz[i], given[i]);
}
console.log("Score: " + score + " / " + quiz.length);

Question 2 is wrong on purpose: the TypeScript compiler is tsc, not node. The report isScore: 3 / 4 every time you run this file.

Common mistakes

• Letting the given-answer array run shorter than the quiz. Then given[i] isundefined. Check that both length values match, or store the reply on the interface.
• Scoring with = instead of ===. Assignment does not compare strings.
• Printing the expected answer before the player replies, then wondering why the quiz is not a quiz. Keep the key inside the object and print it only on a miss, as above, or hide it until you add typed input.
• Mixing spaces in answers. "Paris " with a trailing space is not "Paris".

Practice

1. Change the second given answer from node to tsc and confirm the score becomes 4 / 4.
2. Add a fifth question about interface and a matching given reply that is correct.
3. Print a percent: 100 * score / quiz.length, and if a given array is shorter than the quiz, print an error and skip scoring.

Next project: a library catalog you can search by author.