[Xeoncross]

I was playing with my own Proof-of-work a couple years ago with a pause every X ms so we don't lock the browser while doing the calculations. If someone want's a simple introduction to basic hashing on the clientside here is a simple implementation: https://gist.github.com/Xeoncross/d5a9482e5231db62fb87

coin-hive/Monero would solve a lot of issues with simple MD5/SHA1 implementations like mine (like bot GPU's blowing through any kind of hashcash challenge).