移动端常见menu移动置顶

<div id="brandNameAnchor"></div>   //站位层 初始高度0
<div id="brandName"></div>  //menu 
$(document).ready(function() {
        var $window = $(window);
        var brandName = $('#brandName')
        var brandNameAnchor = $('#brandNameAnchor');
        $window.scroll(function() {
            var window_top = $window.scrollTop();
            var div_top = brandNameAnchor.offset().top;
            if (window_top > div_top) {
                brandName.addClass('stick');
                brandNameAnchor.height(brandName.height());  //menu悬浮后 站位层高度等于menu层高度顶替原位置
            } else {
                brandName.removeClass('stick');
                brandNameAnchor.height(0);
            }
        });
    });