Written in one rage burst after finding that browsers only provide promises (the most absurd interface I could think of for such a job, only a committee or someone insanely obsessed with promises would be able to come up with that).

Written by reading specs, tested a bit but not much... YMMV.

Speed is decent for my use.

 sha256(data) → digest

 let s = sha256();
 s.add(data);
 s.digest() → digest

The returned digest is an Uint8Array instance of 32 bytes with a stapled on addition of a .hex() method returning a string.

Input is expected to be a string (converted to utf-8 for hashing) or an Uint8Array object (or anything for which .forEach behaves in a similar way).

As a convenience HMAC-SHA256 is also implemented