<script>

 // 面向对象

     function Question(theQuestion, theChoices, theCorrectAnswer) {

         // Initialize the instance properties​

         this.question = theQuestion;

         this.choices = theChoices;

         this.correctAnswer = theCorrectAnswer;

         this.userAnswer = "";

         // private properties: these cannot be changed by instances​

         var newDate = new Date(),

         // Constant variable: available to all instances through the instance method below. This is also a private property.​

         QUIZ_CREATED_DATE = newDate.toLocaleDateString();

         // This is the only way to access the private QUIZ_CREATED_DATE variable ​

         // This is an example of a privilege method: it can access private properties and it can be called publicly​

         this.getQuizDate = function () {

             return QUIZ_CREATED_DATE;

         };

         // A confirmation message that the question was created​

         console.log("Quiz Created On: " + this.getQuizDate());

     }

     //Add Prototype Methods to The Question Object

      // Define the prototype methods that will be inherited​

     Question.prototype.getCorrectAnswer = function () {

         return  this.correctAnswer;

     };

     Question.prototype.getUserAnswer = function () {

         return this.userAnswer;

     };

     Question.prototype.displayQuestion = function () {

         var questionToDisplay = "<div class='question'>" + this.question + "</div><ul>";

             choiceCounter = 0;

             this.choices.forEach(function (eachChoice)  {

             questionToDisplay += '<li><input type="radio" name="choice" value="' + choiceCounter + '">' + eachChoice + '</li>';

             choiceCounter++;

         });

         questionToDisplay += "</ul>";

         console.log (questionToDisplay);

     }; 

     function inheritPrototype(childObject, parentObject) {

        // As discussed above, we use the Crockford’s method to copy the properties and methods from the parentObject onto the childObject​

     // So the copyOfParent object now has everything the parentObject has ​

         var copyOfParent = Object.create(parentObject.prototype);

         //Then we set the constructor of this new object to point to the childObject.​

     // Why do we manually set the copyOfParent constructor here, see the explanation immediately following this code block.​

         copyOfParent.constructor = childObject;

         // Then we set the childObject prototype to copyOfParent, so that the childObject can in turn inherit everything from copyOfParent (from parentObject)​

        childObject.prototype = copyOfParent;

     }

     // Child Questions (Sub Classes of the Question object)

     // First, a Multiple Choice Question:

     // Create the MultipleChoiceQuestion​

     function MultipleChoiceQuestion(theQuestion, theChoices, theCorrectAnswer){

     // For MultipleChoiceQuestion to properly inherit from Question, here inside the MultipleChoiceQuestion constructor, we have to explicitly call the Question constructor​

     // passing MultipleChoiceQuestion as the this object, and the parameters we want to use in the Question constructor:​

         Question.call(this, theQuestion, theChoices, theCorrectAnswer);

     };

     // inherit the methods and properties from Question​

     inheritPrototype(MultipleChoiceQuestion, Question);

     // A Drag and Drop Question

     // Create the DragDropQuestion​

     function DragDropQuestion(theQuestion, theChoices, theCorrectAnswer) {

         Question.call(this, theQuestion, theChoices, theCorrectAnswer);

     }

     // inherit the methods and properties from Question​

     inheritPrototype(DragDropQuestion, Question);

     // Overriding Methods

     DragDropQuestion.prototype.displayQuestion = function () {

         // Just return the question. Drag and Drop implementation detail is beyond this article​

         console.log(this.question);

     };

     // Initialize some questions and add them to an array​

     var allQuestions = [

     new MultipleChoiceQuestion("Who is Prime Minister of England?", ["Obama", "Blair", "Brown", "Cameron"], 3),

     new MultipleChoiceQuestion("What is the Capital of Brazil?", ["São Paulo", "Rio de Janeiro", "Brasília"], 2),

     new DragDropQuestion("Drag the correct City to the world map.", ["Washington, DC", "Rio de Janeiro", "Stockholm"], 0)

     ];

     // Display all the questions​

     allQuestions.forEach(function (eachQuestion)  {

         eachQuestion.displayQuestion();

     });

 </script>