function compare(arr, arr2) {
var l = arr.length;
for(var i = 0; i < l; ++i)
for(var a in arr[i])
if(arr2[i][a] !== arr[i][a]) return [i, a, arr[i][a], arr2[i][a]];
return false;
}$('.block').on('click', function() {
var _this = $(this);
var parent = _this.parent();
var el = parent.find('.block:not(.hidden)').toggleClass('hidden');
if(el[0] == parent.find('.block').last()[0]) parent.find('.block').first().toggleClass('hidden');
else el.next('.block').toggleClass('hidden');
})$('#nav').on('click', function() {
$(this).slideToggle()
}let els = document.getElementsByClassName('...');
Array.from(els).forEach((el) => if(!el.value) el.style.border = '1px solid red');
// Или
for(let i = 0; i < els.length; ++i) if(!el.value) els[i].style.border = '1px solid red')