We have to remember that the current WASM spec is still "just" a MVP. It doesn't yet include performance related spec (like SMID).
WASM is also fairly recent. JS interpreter/JIT in browser has seen years of optimization with a trove of real world usage. It will take some time for WASM to be able to compete seriously.
Another factor is also that the WASM compilers for various languages (Rust, C/C++, etc) are obviously recent too and not super optimized.
My own tiny experiment is that WASM can already yield quite decent performance gain but with very compute intensive load, which is not a typical problem in frontend development.
The size gain is also real, but you need to handcraft your WASM or forget about using the std and other stuff in the language you are compiling from (Rust generate very fat binary with a naïve implementation for example).
Still, I am quite optimistic about WASM. I was actually impressed that, even though it is quite recent, I can already compete with JS when it come to performance. When the various performance-related spec will be finalized and implemented and that browsers and compilers start heavily optimizing the WASM, we should really see some real-world gain.
Another factor is also that the WASM compilers for various languages (Rust, C/C++, etc) are obviously recent too and not super optimized.
My own tiny experiment is that WASM can already yield quite decent performance gain but with very compute intensive load, which is not a typical problem in frontend development. The size gain is also real, but you need to handcraft your WASM or forget about using the std and other stuff in the language you are compiling from (Rust generate very fat binary with a naïve implementation for example).
Still, I am quite optimistic about WASM. I was actually impressed that, even though it is quite recent, I can already compete with JS when it come to performance. When the various performance-related spec will be finalized and implemented and that browsers and compilers start heavily optimizing the WASM, we should really see some real-world gain.