> Not many people are going to want to be rolling their own libc like that author.

Emscripten provides a libc implementation based on musl, and so does wasi-libc (https://github.com/WebAssembly/wasi-libc).

If you explicitly list which functions you want to export from your WebAssembly module, the linker will remove all the unused code, in the same way that "tree-shaking" works for JS bundlers.

In my experience, a WebAssembly module (even with all symbols exported) is smaller than the equivalent native library. The bytecode is denser.

WebAssembly modules tend to be larger than JavaScript because AOT-compiled languages don't care as much about code size--they assume you only download the program/library once. In particular, LLVM (which I believe is the only mainstream WebAssembly-emitting backend) loves inlining everything.

Judicious use of `-Oz`, stripping debug info, and other standard code size techniques really help here. The app developer does have to care about code size, of course.