getWasmBytes contains the lines:

if (typeof window !== 'undefined' && typeof atob === 'function')
  return Uint8Array.from(atob(binary), x => x.charCodeAt(0));
return Buffer.from(binary, 'base64');

In a web worker, window is undefined, but Buffer is not available either. The condition should be updated to pass inside web workers. I’m happy to open a PR, but I wasn’t sure what the best detection mechanism was. Maybe (typeof window !== 'undefined' || typeof self !== 'undefined') && typeof atob === 'function'?