JavaScript accordion sans jQuery

Demo

HTML

<div id="accordion">
    <h4 class="accordion-toggle">Accordion 1</h4>
    <div class="accordion-content default">
        <p>Cras malesuada ultrices augue molestie risus.</p>
    </div>
    <h4 class="accordion-toggle">Accordion 2</h4>
    <div class="accordion-content">
        <p>Lorem ipsum dolor sit amet mauris eu turpis.</p>
    </div>
    <h4 class="accordion-toggle">Accordion 3</h4>
    <div class="accordion-content">
        <p>Vivamus facilisisnibh scelerisque laoreet.</p>
    </div>
</div>

CSS

.accordion-toggle {
    cursor: pointer;
}
.accordion-content {
    display: none;
}
.accordion-content.default {
    display: block;
}

JavaScript

// https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/filter#Polyfill
if (!Array.prototype.filter) {
    Array.prototype.filter = function(fun/*, thisArg*/) {
        'use strict';

        if (this === void 0 || this === null) {
            throw new TypeError();
        }

        var t = Object(this);
        var len = t.length >>> 0;
        if (typeof fun !== 'function') {
            throw new TypeError();
        }

        var res = [];
        var thisArg = arguments.length >= 2 ? arguments[1] : void 0;
        for (var i = 0; i < len; i++) {
            if (i in t) {
                var val = t[i];

                // NOTE: Technically this should Object.defineProperty at
                //       the next index, as push can be affected by
                //       properties on Object.prototype and Array.prototype.
                //       But that method's new, and collisions should be
                //       rare, so use the more-compatible alternative.
                if (fun.call(thisArg, val, i, t)) {
                    res.push(val);
                }
            }
        }

        return res;
    };
}

(function() {
    "use strict";
    // Stolen from: https://toddmotto.com/ditch-the-array-foreach-call-nodelist-hack/
    var forEach = function(array, callback, scope) {
        for (var i = 0; i < array.length; i++) {
            callback.call(scope, i, array[i]);
        }
    },
        accordion = document.getElementById("accordion"),
        toggles = accordion.querySelectorAll(".accordion-toggle"),
        greedy = false;
    forEach(toggles, function(i, v) {
        v.addEventListener("click", function() {
            var content = this.nextElementSibling;
            var classes = content.className.split(" ");
            if (classes.indexOf("default") !== -1) {
                content.className = classes.filter(function(value){
                    return value !== "default"
                }).join(" ");
            } else {
                if (greedy) {
                    forEach(toggles, function(i, toggle) {
                        var ct = toggle.nextElementSibling;
                        var cs = ct.className.split(" ");
                        ct.className = cs.filter(function(value){
                            return value !== "default"
                        }).join(" ");
                    });
                }
                content.className += " default";
            }
        }, false);
    });
})();