设置select2多选排序

$select.off().on("select2:select", function (evt) {
	var element = evt.params.data.element;
	var $element = $(element);
	$element.detach();
	var slectedL = $select.find("option:selected").length;
	if(slectedL<1){
		$select.prepend($element);
	 }else{
		$select.find("option:eq("+ (slectedL-1) +")").after($element);
	}
	$select.trigger("change");
}).on("select2:unselect", function (evt) {
	var element = evt.params.data.element;
	var $element = $(element);
	$element.detach();
	$select.append($element);
});