function initScript() {
    addClass({
            tagName: 'a',
            tagClass: 'a-class',
            classAdd: 'parent',
            addToParent: true
        });
}

function addClass (_options) {
    var _tagName = _options.tagName;
    var _tagClass = _options.tagClass;
    var _classAdd = _options.classAdd;
    var _addToParent = false || _options.addToParent;
    var _el = document.getElementsByTagName(_tagName);
    if (_el) {
        for (var i=0; i < _el.length; i++) {
            if (_el[i].className.indexOf(_tagClass) != -1) {
                _el[i].onclick = function() {
                    if (_addToParent) {
                        if (this.parentNode.className.indexOf(_classAdd) == -1) {
                            this.parentNode.className += ' ' + _classAdd;
                        } else {
                            this.parentNode.className = this.parentNode.className.replace(_classAdd, '');
                        }
                    } else {
                        if (this.className.indexOf(_classAdd) == -1) {
                            this.className += ' ' + _classAdd;
                        } else {
                            this.className = this.className.replace(_classAdd, '');
                        }
                    }
                    return false;
                };
            }
        }
    }
}
if (window.addEventListener)
    window.addEventListener("load", initScript, false);
else if (window.attachEvent)
    window.attachEvent("onload", initScript);