From my experience, WASM is great for easily porting existing codebases to the browser. It took me less than a day to download Emscripten, learn a little about WASM, make one toy project, and then port a 20-year-old, 40-KLOC C++ project to the browser [1]. The last part only took me half an hour, and I don't even write C++.
[1] https://poincare.matf.bg.ac.rs/~janicic/gclc/