How do I speed up Dark mode delay on website?

I would like to speed up dark mode taking effect on my website. When I load a page currently there is a delay between the page loading and dark mode taking effect. Here is my jQuery.js code

onload = function () {
  if (localStorage.getItem("darkMode") === "true") {
    var mode = localStorage.getItem("darkMode");
    enableDarkMode();
  }
}

function enableDarkMode() {
  $("body").addClass("dark");
  $("nav").removeClass("navbar navbar-expand-md navbar-light");
  $("nav").addClass("navbar navbar-expand-md navbar-dark");
  $('.inner-switch').text("ON");
  var mode = localStorage.setItem("darkMode", "true");
}

function disableDarkMode() {
  $("body").removeClass("dark");
  $("nav").removeClass("navbar navbar-expand-md navbar-dark");
  $("nav").addClass("navbar navbar-expand-md navbar-light");
  $('.inner-switch').text("OFF");
  var mode = localStorage.setItem("darkMode", "false");
}

$('.inner-switch').on("click", function () {
  if ($("body").hasClass("dark")) {
    disableDarkMode();
  } else {
    enableDarkMode();
  }
});