Notes

var quiz = (function(){

var q1 = new Question('Which city is the capital of America?' ['Washingtom', 'New York', 'Stanford'], 0);
var q2 = new Question('When did Pakistan come into being?', ['1856', '1947', '1971'], 1);
var q3 = new Question('How many days are in a week?', [30, 10, 7], 2);

var questions = [q1, q2, q3];
var numOfQuestions = questions.length;
var randomQuestion;
var selectedOption;
var score = 0;

function Question(question, options, answer){
this.question = question;
this.options = options;
this.answer = answer;
}

function selectRandomQuestion(){
randomQuestion = questions[Math.floor(Math.random() * numOfQuestions)];
}

function logToConsole(){
console.log(randomQuestion.question);
for(var i = 0; i < randomQuestion.options.length; ++i)
console.log(i + ". " + randomQuestion.options[i]);
}

function takeInput(){
selectedOption = prompt("Choose the correct answer: ");
if(selectedOption == 'exit') return 0;
else return 1;
}

function checkAnswer(){
if(parseInt(selectedOption) == randomQuestion.answer){
console.log('Correct answer!!');
++score;
}
else{
console.log('Wrong answer!!!');
--score;
}
}


return {
addQuestion: function(question, options, answer){
Question(question, options, answer);
},
selectQuestion: function(){
selectRandomQuestion();
},
printQuestion: function(){
logToConsole();
},
input: function(){
return takeInput();
},
verify: function(){
checkAnswer();
},
displayScore: function(){
console.log('Score: ' + score);
}
}


})();

alert('Type exit if you want to exit the quiz!!');

while(true){

quiz.selectQuestion();
quiz.printQuestion();
if(quiz.input() == 0) break;
quiz.verify();
quiz.displayScore();

}

alert('Goodbye!!!');