I do a lot of numerical work in Javascript, and I typically find Safari to be the fastest JavaScript engine on my machine for the code I try (sometimes about the same or sometimes several times faster). Safari’s Javascript performance is pretty impressive.

Web Assembly is a new and rapidly changing feature. SIMD support in Web Assembly is even newer. Neither one has yet been adopted by most websites / web applications.

In a few years I would expect more developers to start adopting these technologies and Safari to have finally gotten around to a SIMD implementation.

Personally I hope the browsers all figure out how to get double-precision FMA operations (fused multiply-add) in wasm.