Software entities (classes, modules, functions, etc.) should be open for extension but closed for modification.
软件实体（类，模块，方法等等）应当对扩展开放，对修改关闭，即软件实体应当在不修改的前提下扩展。

// 问题类型
var AnswerType = {
    Choice: 0,
    Input: 1
};

// 问题实体
function question(label, answerType, choices) {
    return {
        label: label,
        answerType: answerType,
        choices: choices // 这里的choices是可选参数
    };
}

var view = (function () {
    // render一个问题
    function renderQuestion(target, question) {
        var questionWrapper = document.createElement('div');
        questionWrapper.className = 'question';

        var questionLabel = document.createElement('div');
        questionLabel.className = 'question-label';
        var label = document.createTextNode(question.label);
        questionLabel.appendChild(label);

        var answer = document.createElement('div');
        answer.className = 'question-input';

        // 根据不同的类型展示不同的代码：分别是下拉菜单和输入框两种
        if (question.answerType === AnswerType.Choice) {
            var input = document.createElement('select');
            var len = question.choices.length;
            for (var i = 0; i < len; i++) {
                var option = document.createElement('option');
                option.text = question.choices[i];
                option.value = question.choices[i];
                input.appendChild(option);
            }
        }
        else if (question.answerType === AnswerType.Input) {
            var input = document.createElement('input');
            input.type = 'text';
        }

        answer.appendChild(input);
        questionWrapper.appendChild(questionLabel);
        questionWrapper.appendChild(answer);
        target.appendChild(questionWrapper);
    }

    return {
        // 遍历所有的问题列表进行展示
        render: function (target, questions) {
            for (var i = 0; i < questions.length; i++) {
                renderQuestion(target, questions[i]);
            };
        }
    };
})();

var questions = [
                question('Have you used tobacco products within the last 30 days?', AnswerType.Choice, ['Yes', 'No']),
                question('What medications are you currently using?', AnswerType.Input)
                ];

var questionRegion = document.getElementById('questions');
view.render(questionRegion, questions);

function questionCreator(spec, my) {
    var that = {};

    my = my || {};
    my.label = spec.label;

    my.renderInput = function () {
        throw "not implemented"; 
        // 这里renderInput没有实现，主要目的是让各自问题类型的实现代码去覆盖整个方法
    };

    that.render = function (target) {
        var questionWrapper = document.createElement('div');
        questionWrapper.className = 'question';

        var questionLabel = document.createElement('div');
        questionLabel.className = 'question-label';
        var label = document.createTextNode(spec.label);
        questionLabel.appendChild(label);

        var answer = my.renderInput();
        // 该render方法是同样的粗合理代码
        // 唯一的不同就是上面的一句my.renderInput()
        // 因为不同的问题类型有不同的实现

        questionWrapper.appendChild(questionLabel);
        questionWrapper.appendChild(answer);
        return questionWrapper;
    };

    return that;
}

function choiceQuestionCreator(spec) {

    var my = {},
that = questionCreator(spec, my);
            
    // choice类型的renderInput实现
    my.renderInput = function () {
        var input = document.createElement('select');
        var len = spec.choices.length;
        for (var i = 0; i < len; i++) {
            var option = document.createElement('option');
            option.text = spec.choices[i];
            option.value = spec.choices[i];
            input.appendChild(option);
        }

        return input;
    };

    return that;
}

function inputQuestionCreator(spec) {

    var my = {},
that = questionCreator(spec, my);

    // input类型的renderInput实现
    my.renderInput = function () {
        var input = document.createElement('input');
        input.type = 'text';
        return input;
    };

    return that;
}

var view = {
    render: function(target, questions) {
        for (var i = 0; i < questions.length; i++) {
            target.appendChild(questions[i].render());
        }
    }
};

var questions = [
    choiceQuestionCreator({
    label: 'Have you used tobacco products within the last 30 days?',
    choices: ['Yes', 'No']
　　}),
    inputQuestionCreator({
    label: 'What medications are you currently using?'
　　})
    ];

var questionRegion = document.getElementById('questions');

view.render(questionRegion, questions);