fetch jsonp with a modern API

fetch-jsonp.js

/**
 * @param {string} url
 */
function fetchJSONP(url) {
  return new Promise((accept, reject) => {
    const req = `jsonp${String(Math.random()).replace(".", "_")}`;
    const scr = document.createElement("script");
    scr.src = url + `&callback=${req}`;
    scr.onerror = cleanup;
    document.head.append(scr);

    const timeout = setTimeout(() => {
      cleanup();
      reject(new Error("Timeout"));
    }, 5000);

    /// @ts-ignore
    window[req] = data => {
      cleanup();
      accept(data);
    };

    function cleanup() {
      /// @ts-ignore
      delete window[req];
      clearTimeout(timeout);
      scr.remove();
    }
  });
}