You shouldn’t ever need to deal with OsString itself on wasm32-unknown-unknown, since that target basically just doesn’t cover functionality that needs it, but the actual situation is genuinely worse than OsString: Rust insists on valid Unicode (as is right and proper), but the web suffers from the affliction of ill-formed UTF-16. If you blindly convert from JavaScript strings to Rust strings, you will encounter data and functionality loss in a few situations, in practice always involving IME (or similar) text entry on Windows. The first bug I filed about this: https://github.com/Pauan/rust-dominator/issues/10, and you can follow further links if you’re interested. IE and Edge used to be largely immune to this, but IE is dead and I suppose Edge will have regressed in this way with the Chromium migration, since the bug filed in Chromium a few years ago <https://bugs.chromium.org/p/chromium/issues/detail?id=949056> has languished. (Firefox too, with <https://bugzilla.mozilla.org/show_bug.cgi?id=1541349>.) In the worst-case scenario, careless use like was the case in rust-dominator will mean that some users typing with particular software in a language that’s outside the Basic Multilingual Plane will not be able to type anything.