Autovectorization is hard and fragile in the best of times -- tight stable loops with no (or few) branches and little&#x2F;no memory access that may be aliased, etc.<p>For a dynamic language JIT this is pretty much infeasible (as I understand it). Every loop might have branches for guards&#x2F;bailing out due to deopts, and at least in JS, TypedArrays are allowed to alias eachother.