Funny idea: a long form journalism site could intentionally and openly embed such a script, allowing readers to make "micropayments" of lent CPU time to the site while they read articles.
1. It would not make sense to run on mobile.
2. Mining this way is inefficient, so if the site gets one penny worth of work done, it costs me five pennies.
3. Unless readers have decent GPUs, it's probably not enough money.
Mining is not only inefficient when implemented in JS (even with the web asm stuff, many clients have no support), or when it runs on crappy or old hardware, it also depends on what your electricity costs. Pro-miners put their farms in locations where electricity is super cheap, often in the middle of nowhere, perhaps near a hydro dam. Most clients are on a laptop or mobile in a city, where electricity is much more expensive, and their electric efficiency is made worse because they run it off battery.
Distributed crypto-mining for micropayments via embedded JS is such a huge waste, I'd probably have more problems if I knew the site was doing that, for the guilt of wasting that electricity while reading, just so the author can inefficiently receive a few fractions of a cent. I might even (gasp) rather watch a video ad instead.
How would such a site make its battery-draining nature clear? And why would it do so, given how many people would leave immediately?