WordPressで上部にパーセンテージ表示のスクロール読み込みプログレスバーを実装

<div id="load"></div>

#load {
    background-color: #ff6651;
    height: 3px;
    width: 0px;
    position: fixed;
    left: 0px;
    top: 0px;
    z-index: 9999;
}

$(function() {
    function scroll_fn() {
        let document_height = $(document).height();
        let scroll_so_far = $(window).scrollTop();
        let window_height = $(window).height();
        let max_scroll = document_height - window_height;
        let scroll_percentage = scroll_so_far / (max_scroll / 100);
        $('#load').width(scroll_percentage + '%');
    }
    $(window).scroll(function() {
        scroll_fn();
    });
    $(window).resize(function() {
        scroll_fn();
    });
});