> To get good performance, don't WebAssembly implementations need to use JIT-compilation internally?
No. JITs are great when you're executing code which is very dynamic in nature (either because of dynamic types, or because you're using a lot of interfaces) because the JIT can make use of speculative optimizations based on runtime information.
WASM, however, doesn't really support the notion of compound types and the few types that are supported (int32, int64, float32 and float64) is required to be specified up front. WASM doesn't really have the notion of of ad-hoc polymorphism either. In other words, there's very little for a JIT to speculate about, and so there aren't much insight a JIT can get from having runtime information available. This might change as newer features are added to WASM in the future.
No. JITs are great when you're executing code which is very dynamic in nature (either because of dynamic types, or because you're using a lot of interfaces) because the JIT can make use of speculative optimizations based on runtime information.
WASM, however, doesn't really support the notion of compound types and the few types that are supported (int32, int64, float32 and float64) is required to be specified up front. WASM doesn't really have the notion of of ad-hoc polymorphism either. In other words, there's very little for a JIT to speculate about, and so there aren't much insight a JIT can get from having runtime information available. This might change as newer features are added to WASM in the future.