JavaScript is JIT compiled, it has to be parsed, typechecked, interpreted and eventually compiled. WebAssembly is parsed and then translated to machine code (wi

JavaScript is JIT compiled, it has to be parsed, typechecked, interpreted and eventually compiled. WebAssembly is parsed and then translated to machine code (with a much simpler compilation pipeline). Typical JavaScript VMs have a lot of fast paths for small scripts which also benefits small benchmarks like this. For more realistic workloads, parsing and compiling takes a significant amount of time and you could skip (almost) all of it by precompiling to WebAssembly (not at the moment, since you can't generate JavaScript objects from WebAssembly yet, but that'll happen eventually). JavaScript in particular also has the problem that its semantics is an utterly horrifying mess... This forces the generated code to be very conservative and include a lot of dynamic checks and escape hatches to the interpreter. If anything, the situation is worse than with Lua, and let me remind you that LuaJIT doesn't actually compile said "escape hatches" because of code size. There are just that many of them.