WASM + File System API + output

[erdalkaraca]

I just experimented with the esbuild WASM module and was able to resolve paths to local file system using the File Access API.
What I am missing: how to control esbuild to write output files directly to my file sys handle. Essentially, I am missing a build.onOutput() callback. I think it would be better to stream the output using this callback than providing in-memory buffers in the build result.
Any thoughts?