The entire npm package is 4.5 MBs uncompressed, and that includes a lot of files that won't be included in a modern bundle. A simple `npx esbuild --bundle ./node_modules/rxjs/dist/esm/index.js --outfile=./vendor/rxjs.js --format=esm` gives me a 141 kb file before compression.

If you are seeing 18 MBs in your bundle from npm you may have more than copy or something else wrong.

I will complain that RxJS still doesn't have a proper ESM build in 2026 for even better tree-shaking because that is apparently waiting on the WICG Observables "Proposal" to complete, and cynically I still don't think it is going to happen and I would love real ESM from RxJS someday like yesterday.

> RXJS is also 18 MB

This is impossible. I think you are off by about a factor of 1000.