// mění parametry v url
	function changeParam(paramname, mode) {
		var location = new String(window.location)
			if (paramname == 'producer') {
				var frm = document.getElementById('product_list_bar');
				var els = frm.getElementsByTagName('input');
				var producers = '';
				var each = null;
				for(var el_key in els) {
					each = els[el_key];	
					if (each.name && each.name.indexOf('producer_') == 0) {
						if (each.checked) {
							if (producers.length != 0) {
								producers += ',';
							}
							producers += each.name.substring(9);
						}
					}
				}
				if (producers.length == 0) {
					producers = '0';
				}
				
				mode = producers;
				
			}
		if (mode != -1) {
			if (location.match(paramname)) {
				var replaceexp = new RegExp ('(' + paramname + '=)[,%A-Z0-9]*', 'g')
					location = location.replace(replaceexp, '$1' + mode)
			} else {
				if (location.match(/\?/)) {
					location += '&'
				} else {
					location += '?'
				}
				location = location + paramname + '=' + mode;
			}

		}


		if (paramname == 'producer' || paramname == 'sort') {
			location = firstPage(location)
		};

		window.location = location;
	}

	function firstPage(location) {
		return location.replace(/pageno=[0-9]+&?/, '')
	}

	// parametr funkce je id šipky (vzestupne[0] nebo sestupne[1])
	function sortMode(button) {
		var form = document.product_list_bar
		changeParam('sortmode', parseInt(form.sortmode.value) + parseInt(button))
	}