no-chromium/static/popup.js

async function showNoChromiumPopup() {
  if (navigator.userAgent.includes("Chrome") && localStorage.getItem("no-chromium-popup-shown") != "1") {

    const divPage = document.createElement("div");
    const response = await fetch("https://no-chromium.org/popup/");
    divPage.innerHTML = await response.text();

    for (const child of divPage.querySelectorAll("#no-chromium-head > *")) {
      document.head.appendChild(child);
    }

    for (const child of divPage.querySelectorAll("#no-chromium-body > *")) {
      document.body.appendChild(child);
    }

    document.querySelector("#no-chromium-popup").style = "";
    document.querySelector("#no-chromium-hide-button").addEventListener("click", hideNoChromiumPopup);
  }
}

function hideNoChromiumPopup() {
  document.querySelector("#no-chromium-popup").remove();
  localStorage.setItem("no-chromium-popup-shown", "1");
}

showNoChromiumPopup();