Promise GM.xmlHttpRequest.user.js

// ==UserScript==
// @name     新しいスクリプト 421815
// @version  1
// @match    https://wiki.greasespot.net/GM.xmlHttpRequest
// @match    http://example.com/
// @grant    GM.xmlHttpRequest
// ==/UserScript==

function get(url) {
  return new Promise(resolve => {
    GM.xmlHttpRequest({
      method: "GET",
      url,
      onload: resolve
    });
	})
}

(async () => {
  const response = await get('https://www.google.com/')
  alert(response.responseText)
})()

thanks

Promise style，https://greasyfork.org/en/scripts/457387-douban-gzlib/code