Software entities (classes, modules, functions, etc.) should be open for extension but closed for modification.
軟件實(shí)體（類，模塊,，方法等等）應(yīng)當(dāng)對(duì)擴(kuò)展開(kāi)放,，對(duì)修改關(guān)閉,，即軟件實(shí)體應(yīng)當(dāng)在不修改的前提下擴(kuò)展,。

// 問(wèn)題類型
var AnswerType = {
    Choice: 0,
    Input: 1
};

// 問(wèn)題實(shí)體
function question(label, answerType, choices) {
    return {
        label: label,
        answerType: answerType,
        choices: choices // 這里的choices是可選參數(shù)
    };
}

var view = (function () {
    // render一個(gè)問(wèn)題
    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';

        // 根據(jù)不同的類型展示不同的代碼：分別是下拉菜單和輸入框兩種
        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 {
        // 遍歷所有的問(wèn)題列表進(jìn)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"; 
        // 這里renderInput沒(méi)有實(shí)現(xiàn),，主要目的是讓各自問(wèn)題類型的實(shí)現(xiàn)代碼去覆蓋整個(gè)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();
        // 該render方法是同樣的粗合理代碼
        // 唯一的不同就是上面的一句my.renderInput()
        // 因?yàn)椴煌膯?wèn)題類型有不同的實(shí)現(xiàn)

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

    return that;
}

function choiceQuestionCreator(spec) {

    var my = {},
that = questionCreator(spec, my);
            
    // choice類型的renderInput實(shí)現(xiàn)
    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類型的renderInput實(shí)現(xiàn)
    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);