The binaryen toolkit comes with a wasm2js tool, you could translate the wasm back to js and see how performance compares ;)
It's possible that performance isn't all that different, because asm.js-style Javascript can be surprisingly fast (compared to "idiomatic" human-written Javascript).
Otherwise it's a completely pointless excercise of course, unless you need to support browsers without WASM support (which don't exist anymore AFAIK).
It's unnecessary with AssemblyScript due to AS is just subset of TypeScript and can transpile to ordinal idiomtic javascript. Also AS already uses binaryen under the hood and can produce asm.js via --jsFile, -j command line.
It's possible that performance isn't all that different, because asm.js-style Javascript can be surprisingly fast (compared to "idiomatic" human-written Javascript).
Otherwise it's a completely pointless excercise of course, unless you need to support browsers without WASM support (which don't exist anymore AFAIK).
[1] https://github.com/WebAssembly/binaryen