Besides the "Hey I can write stuff you can't read" factor, what's the point of the array and scientific notation here for the UUID generator[1]?

    var uuid = _ =>
      ( [1e7]+-1e3+-4e3+-8e3+-1e11 ).replace( /[018]/g, c =>
        (c ^ crypto.getRandomValues(new Uint8Array(1))[0] & 15 >> c / 4).toString(16)
      )

The first piece evaluates to the static string '10000000-1000-4000-8000-100000000000'. Writing it using the array toString and scientific notation saves 8 bytes (or 10 if you remove the other whitespace) but is otherwise pointless.

It'd be even better to use '00000000-0000-4000-0000-000000000000' as the "1" and "8" values aren't special. That would let you replace the /[018]/ with just /0/ too.

[1]: https://github.com/Chalarangelo/30-seconds-of-code/blob/mast...