[F12]キーとか押して Console 出して見ろだぜ☆(^~^) 5 とか書いてればOK☆(^~^)
sample1.rs
      fetch('http://warabenture.com/grayscale/blog/setup/sample1.wasm')
        .then((response) => response.arrayBuffer())
        .then((bytes) => WebAssembly.instantiate(bytes, {}))
        .then((results) => {
          const instance = results.instance;
          console.log(instance.exports.sum(2, 3));
        });