To embed code on HN, add 2 or more spaces at the beginning of each line:

  async (() => (e) {
  try { await doSomething();
        while (!done) { ({ done, value } = await reader.read()); }
        promise
        .then(goodA, badA)
        .then(goodB, badB)
        .catch((err) => { console.error(err); }
  catch { } 
  finally { using stack = new DisposableStack();
  stack.defer(() => console.log("done.")); }
  });

(indentation preserved as posted by OP – I don't understand how somebody can code like this either :-)