https://fetch.spec.whatwg.org/

https://developer.mozilla.org/en-US/docs/Web/API/Fetch_API
https://developer.mozilla.org/en-US/docs/Web/API/Fetch_API/Using_Fetch
https://developers.google.com/web/updates/2018/12/background-fetch

2018
https://medium.com/google-developer-experts/background-fetch-api-get-ready-to-use-it-69cca522cd8f
https://medium.freecodecamp.org/a-practical-es6-guide-on-how-to-perform-http-requests-using-the-fetch-api-594c3d91a547
    http://jem-space.ru/praktichieskoie-es6-rukovodstvo-o-tom-kak-sdielat-http-zapros-s-pomoshchiu-fetch-api/
https://medium.com/webbdev/fetch-3d0b811ffcb5