Seeing the same with Chromium on my Linux machine. In Firefox the JS version is really slow, as you would expect.

It's kind of hard to judge this without having a decent enough look at the code, or how it is being benchmarked. For example, asm.js requires quite a bit of set-up to intialise; if it's restarted from scratch every loop for benchmarking purposes that would mess up the timing.

Shader 0.2 - Samsung galaxy s8