将jQuery转换为纯javascript代码

Question

我正在尝试复制this website的导航栏，我已经使用jQuery成功地实现了它，但我需要用普通的javascript重写它

(function ($) {
$(document).ready(function () {
    var $nav1 = $("#nav-1"),
        $nav2 = $("#nav-2"),
        $sticky = $nav1.before($nav2.addClass("fixed").removeClass("hide"));

    $(window).on("scroll", function () {
        var fromTop = $(window).scrollTop();
        $("body").toggleClass("on-scroll", (fromTop > 200));
    });
});
})(jQuery);

这是我尝试用普通的JS重写它，但它不能在atm上工作

(function () {
var nav1 = document.getElementById("nav-1"),
    nav2 = document.getElementById("nav-2"),
    sticky = nav1.insertAdjacentHTML("beforebegin", nav2.outerHTML);

// nav2.className += " fixed";
nav2.classList.add("fixed");
nav2.classList.remove("hide");

window.onscroll = function () {
    var fromTop = window.scrollTop;
    body.classList.toggle("on-scroll", fromTop > 200);
};
}());