app.js

function populate() {
    if(quiz.isEnded()) {
        showScores();
    }
    else{
        // show question
        var element = document.getElementById("question");
        element.innerHTML = quiz.getQuestionIndex().text;

        //show choices
        var choices = quiz.getQuestionIndex().choices;
        for(var i = 0; i< choices.length; i++) {
            var element = document.getElementById("choice" + i);
            element.innerHTML = choices[i];
            guess("btn" + i, choices[i]);
        }

        showProgress();
    }
};

function guess(id, guess) {
    var button = document.getElementById(id);
    button.onclick = function() {
        quiz.guess(guess);
        populate();
    }
}

function showProgress() {
    var currentQuestionNumber = quiz.questionIndex + 1;
    var element = document.getElementById("progress");
    element.innerHTML = "Question " + currentQuestionNumber + " of " + quiz.questions.length;
}

function showScores() {
    var gameoverHtml = "<h1>Result</h1>";
    gameoverHtml += "<h2 id='score'> Your scores: " + quiz.score + "</h2>"
    var element = document.getElementById("quiz");
    element.innerHTML = gameoverHtml;
}


var questions = [
    new Question("Which one is not an object oriented programming language?", ["Java", "C++", "C#", "C"], "C"),
    new Question("Which language is used for styling web pages?", ["XML", "HTML", "CSS", "JQuery"], "CSS"),
    new Question("There are ____ main components of objects oriented programming.", ["1", "6", "2", "4"], "4"),
    new Question("Which language is used for web apps?", ["Javascript", "Python", "PHP", "All"], "All"),
    new Question("MVC is a _______.", ["Language", "Library", "Framework", "All"] , "Framework")
];

var quiz = new Quiz(questions);

populate();