javascript - カウンターインクリメントが動的に機能しない?

Question

以下に示すように、新しい件名が生成されるたびにカウンタ増分番号を動的に変更することは可能ですか?

新しい件名を動的に生成するときにカウンター増分番号が変更されていませんか?

私はまだコーディングが初めてなので、新しいフィドルを提供していただければ幸いです。

フィドル

ありがとう！

HTML:

<button class="button" data-bind="click: addClass">Add a New Class</button>
<button class="button">
Apply
</button>
<hr>

<ul align="center" data-bind="foreach: classes">
    <li>
        <label class="number">Subject:</label><input type="text" data-bind="value: title" placeholder="E.g: English"/>
        <select disabled data-bind="value: credits">
        <option  selected data-bind="value: credits">1</option>
        </select>
        <label>Grade:</label>
        <input type="text" data-bind="value: letterGrade" placeholder="E.g: A+"/>
        <br>
        <br>
    </li>
</ul>



<hr />

<br>
<h4>
Your GPA is: <b><span data-bind="text: totalGPA"></span></b>
</h4>
<br>
<h4>
Final Grade: <span data-bind="text: totalGrade"></span>
</h4>

CSS:

@import url(http://fonts.googleapis.com/css?family=Open+Sans:400,700);
@import url(http://fonts.googleapis.com/css?family=Inconsolata:400);
* { text-rendering: optimizelegibility;}
body, input, textarea, select, button { font-family: 'Open Sans', sans-serif; }
pre { font-family: 'Inconsolata', monospace; }

span {font-size: 18px;}


h1 {font-size: 25px;}



.number {
    counter-reset: subsection;
}

.number:after {
    counter-increment: section;
    content: " " counter(section) ". ";
}

JQuery:

var gradeMapping = {
        'A+': 15,
        'A': 14,
        'A-': 13,
        'B+': 12,
        'B': 11,
        'B-': 10,
        'C+': 9,
        'C': 8,
        'C-': 7,
        'D+': 6,
        'D': 5,
        'D-': 4,
        'E+': 3,
        'E': 2,
        'E-': 1
    }
function Class(title, credits, letterGrade) {
    var self = this;
    self.title = ko.observable(title);
    self.credits = ko.observable(credits);
    self.letterGrade = ko.observable(letterGrade);
    self.gpa = ko.computed(function() {
        return gradeMapping[self.letterGrade()];
    });
}

function GpaCalcViewModel() {
    var self = this;
    self.classes = ko.observableArray();
    self.totalGPA = ko.computed(function() {
        var totalWeightedGPA = 0,
            totalCredits = 0;
        $.each(self.classes(), function() {
            totalWeightedGPA += (this.gpa() * this.credits());
            totalCredits += (this.credits() * 1);
        })
        return totalWeightedGPA / totalCredits;
    });
    self.totalGrade = ko.computed(function() {
        var totalWeightedGPA = 0,
            totalCredits = 0;
        var gradeLetter = null;
        $.each(self.classes(), function() {
            totalWeightedGPA += (this.gpa() * this.credits());
            totalCredits += (this.credits() * 1);
        });
        $.each(gradeMapping, function(letter, number) {
                if(number == Math.round(totalWeightedGPA / totalCredits)){
                gradeLetter = letter;
            }
        })
        return gradeLetter;
    });
    self.addClass = function() {
        self.classes.push(new Class());
    }
};
var viewModel = new GpaCalcViewModel();
ko.applyBindings(viewModel);