That's not a poor design decision but helps to better optimize the compiler.

Perl's way to represent large data blobs in strings surprised me when I first saw it. IMHO this has large implications on character representation and the need for utf8 flags.

If JS wanted to support memory manipulation with peek and poke it could just implement a special object.

Anyway using an array of bytes is already fast enough for your needs.

Btw: You didn't say browser before, if Perl was running inside the browser it wouldn't have file access either.

In general you should be careful with bold assumptions written in bold letters.