Javascript，我如何调整这个js下拉菜单

Question

我希望在我点击它之后关闭下拉菜单，当我点击它之后箭头变成灰色，我希望它一直是相同的颜色（黑色）。

http://codepen.io/anon/pen/YXMaGJ

var dropdown = document.querySelectorAll('.dropdown');
var dropdownArray = Array.prototype.slice.call(dropdown,0);
dropdownArray.forEach(function(el){
    var button = el.querySelector('a[data-toggle="dropdown"]'),
            menu = el.querySelector('.dropdown-menu'),
            arrow = button.querySelector('i.icon-arrow');

    button.onclick = function(event) {
        if(!menu.hasClass('show')) {
            menu.classList.add('show');
            menu.classList.remove('hide');
            arrow.classList.add('open');
            arrow.classList.remove('close');
            event.preventDefault();
        }
        else {
            menu.classList.remove('show');
            menu.classList.add('hide');
            arrow.classList.remove('open');
            arrow.classList.add('close');
            event.preventDefault();
        }
    };
})
Element.prototype.hasClass = function(className) {
    return this.className && new RegExp("(^|\\s)" + className + "(\\s|$)").test(this.className);
};