js实现滚动条下拉到一定程度固定结算栏

var a = $("body").height();
var b = $(window).height();
var c = a - b - $(".footer").height();

$(window).scroll(function() {
    if ($(window).scrollTop() > c) {
        $(".jiesuan-box").css("position", "static");
    } else {
        $(".jiesuan-box").css("position", "fixed");
    }
});