loader.js

let div = document.createElement("div");
div.className = "loader";
div.innerHTML = `<div class="loader-dots">
  <div class="dots"></div>
  <div class="dots"></div>
  <div class="dots"></div>
  <div class="dots"></div>
  <div class="dots"></div>
</div>`;

document.body.classList.add("stop-scrolling");
document.body.appendChild(div);

document.addEventListener('readystatechange', event => {
    if (event.target.readyState === "complete") {
        document.querySelector(".loader").style.display = "none";
        document.body.classList.remove("stop-scrolling");
    }
});