unfetch
Bare minimum 500b fetch polyfill
...One of the key differences is that Unfetch focuses on implementing the fetch() API, while offering minimal (yet functional) support to the other sections of the Fetch spec, like the Headers class or the Response class. Uses simple arrays instead of iterables, since arrays are iterables. No streaming, just Promisifies existing XMLHttpRequest response bodies. Use in Node.JS is handled by isomorphic-unfetch.