[urschrei]

GEOS will be available in WASM sooner or later (if it isn’t already, and if the licence works for you), rust-geo (under active development, I’m one of a few core contributors who work on it) is available compiled to WASM today (you can see a demo from a core contributor at rgis.app). Those are both vector only. For a more mature product that “only” leverages JS, placemark is the state of the art, and is amazing.

I’m not a raster or EO person so I can’t speak to GDAL’s availability, but I’m dubious that the browser is a good interface for that kind of work, or for a full GIS more generally.