The highly optimizable, explicit and precise code for the interpreter is WASM. JS VMs don't need more hints from the code. They need guarantees. They already a

The highly optimizable, explicit and precise code for the interpreter is WASM. JS VMs don't need more hints from the code. They need guarantees. They already analyze and profile JS, but as long as JS is allowed to be dynamic (and it has to, it won't be JS without it), then they have to keep the complexity and cost of all the extra runtime checks and possible deoptimizations.