helper function for web assembly fetch and instantiate

helper.js

function fetchAndInstantiateWasm (url, imports) {
  return fetch(url)
    .then(res => {
      if (res.ok)
        return res.arrayBuffer();
      throw new Error('Unable to fetch Web Assembly file ${url}.');
    })
    .then(bytes => WebAssembly.compile(bytes))
    .then(module => WebAssembly.instantiate(module, imports || {}))
    .then(instance => instance.exports);
}

fetchAndInstantiateWasm('./program.wasm')
.then(m => {
  window.getSqrt = m.getSqrt;
});