$(".nav-link").click(function () {
  // If the clicked element has the active class, remove the active class from EVERY .nav-link>.state element
  if ($(this).hasClass("active")) {
    $(".nav-link").removeClass("active");
  }
  // Else, the element doesn't have the active class, so we remove it from every element before applying it to the element that was clicked
  else {
    $(".nav-link").removeClass("active");
    $(this).addClass("active");
  }
});