<!DOCTYPE html>
<html class="nojs">
    {% include head.html %}
    {% if page.url == "/index.html" %} <body> {% else %} <body class="on-post"> {% endif %}
        {% include header.html %}

        {{ content }}

        <script src="/assets/bower_components/system.js/dist/system.js"></script>
        <script>
            /* global System */
            System.config({
                baseURL   : '/assets/js',
                map       : {
                    traceur: '/assets/bower_components/traceur/traceur.js',
                    json   : '/assets/bower_components/plugin-json/json.js'
                },
                transpiler: 'traceur',
                globalEvaluationScope: false
            });

            System.import('main.js');
        </script>
    </body>
</html>

<!DOCTYPE html>
<html class="nojs">
    {% include head.html %}
    <body>
        {% include header.html %}

        {{ content }}

        <script src="/assets/bower_components/system.js/dist/system.js"></script>
        <script>
            /* global System */
            System.config({
                baseURL   : '/assets/js',
                map       : {
                    traceur: '/assets/bower_components/traceur/traceur.js',
                    json   : '/assets/bower_components/plugin-json/json.js'
                },
                transpiler: 'traceur',
                globalEvaluationScope: false
            });

            System.import('main.js');
        </script>
    </body>
</html>

Remove on-post detection from jekyll
Remove on-post detection from jekyll