Can anyone recommend a library for reading/writing files from the browser? I'm trying to target javascript from a multiplatform app and I just discovered that Okio (which I'm currently using) doesn't support filesystem access in the browser.

AFAIK you can't write files in the browser. You can't open or list files either, the user has to provide you with a file handle that you can read.

That's not true any more https://developer.mozilla.org/en-US/docs/Web/API/FileSystem

Interesting. Well, that's a good idea for a multiplatform library, then