[danik.js]

var links = document.querySelectorAll('a');
var toggle = function() {
    var showed = this.querySelector('.show');
    var closed = this.querySelector('.close');
    showed.className = 'close';
    closed.className = 'show';
};
for (var i = 0; i < links.length; i++) {
    links[i].onclick = toggle;
}