maybeInstantiateStreaming.js

async function maybeInstantiateStreaming(path, ...opts) {
  // Start the download asap.
  const f = fetch(path);
  try {
    // This will throw either if `instantiateStreaming` is
    // undefined or the `Content-Type` header is wrong.
    return WebAssembly.instantiateStreaming(
      f,
      ...opts
    );
  } catch(_e) {
    // If it fails for any reason, fall back to downloading
    // the entire module as an ArrayBuffer.
    return WebAssembly.instantiate(
      await f.then(f => f.arrayBuffer()),
      ...opts
     );
  }
}