Trouble pushing to Array.

// Question.js

function Question(question) {
    this.question = question;
    return question;
}

Question.prototype.toHTML = function(question) {
    var htmlString = question;
    return htmlString;
};

// Quiz.js

function Quiz() {
    this.questions = [];
    this.currentQuestionIndex = 0;
    console.log(this.questions);
}

// Adds new question to array
Quiz.prototype.add = function(newQuestion) {
    this.questions.push(newQuestion);
};

// App.js

// Create quiz
var quiz = new Quiz();

// Create Questions
var question1 = new Question('What is 2 + 2?');
var question2 = new Question('What is the capitol of the United States?');

// Add Questions
quiz.add(question1);
quiz.add(question2);