var links = document.querySelectorAll('a');
console.log(links);
function show(event) {
    if (this.nextElementSibling.style.visibility === 'hidden') {
        this.nextElementSibling.style.visibility = 'visible';
    }
    else {
        this.nextElementSibling.style.visibility = 'hidden';
    }
}
for (var i = 0; i < links.length; i++) {
    links[i].addEventListener('click', show);
}