$ в названии переменной - jQuery

При сжатии js скрипта выпадает ошибка:

SyntaxError: Unexpected token: name ($content)

До сжатия скрипт работает нормально.

(function () {
let $content = $('.s-content');
let $back2top = $('.back-to-top');
let $windowHeight;
let contentBottom;
function onScrollWindow() {
    let offsetY = window.pageYOffset;
    if (offsetY - $content.offset().top > 100 && !$back2top.hasClass('back-to-top_visible')) {
        $back2top.addClass('back-to-top_visible');
    } else {
        if (offsetY - $content.offset().top < 100 && $back2top.hasClass('back-to-top_visible')) {
            $back2top.removeClass('back-to-top_visible');
        }
    }
    if (offsetY + $windowHeight >= contentBottom && !$back2top.hasClass('back-to-top_pinned')) {
        $back2top.addClass('back-to-top_pinned');
    } else {
        if (offsetY + $windowHeight < contentBottom && $back2top.hasClass('back-to-top_pinned')) {
            $back2top.removeClass('back-to-top_pinned');
        }
    }
}
function onResizeWindow() {
    $windowHeight = $(window).height();
    contentBottom = $content.offset().top + $content.height() + 25;
}
$(document).ready(function () {
    if ($content.length < 1 || $back2top.length < 1) {
        return;
    }
    $windowHeight = $(window).height();
    contentBottom = $content.offset().top + $content.height() + 25;
    document.addEventListener('scroll', function () {
        onScrollWindow();
    }, true);
    window.addEventListener('resize', function () {
        onResizeWindow();
    }, true);
}); 
    })();