JSFiddle - React, Tailwind, and code Playground

HTML

<script src="jquery.min.js"></script>
<script src="jquery-latest.js"></script>
<div id="input">
        <div class="feature draggable">Drag 1</div>
        <div class="feature resizable">Resize</div>
        <div class="feature downloadable">Download</div>
        <div class="feature draggable">Drag 2</div>
        <div class="feature trackable">Track</div>
        <div class="feature colorable">Color</div>
    </div>

JavaScript

(function($) {
    $.fn.classes = function(f) {
        var c = [];
        $.each(this, function(i, v) {
            var _ = v.className.split(/\s+/);
            for (var j in _)'' === _[j] || c.push(_[j]);
        });
        c = $.unique(c);
        if ("function" === typeof f) for (var j in c) f(c[j]);
        return c;
    };
})(jQuery);

$(document).ready(function() {
    alert($('#input div').classes());
});