[ruslan_mart]

(function() {
	var header = document.getElementById('header'),
		headerIsFixed = false,
		headerTop = header.getBoundingClientRect().top;
	
	window.addEventListener('scroll', function() {
		if(this.pageYOffset >= headerTop != headerIsFixed) {
			headerIsFixed = !headerIsFixed;
			header.classList[headerIsFixed ? 'add' : 'remove']('fixed');
		}
	});
})();