async resolves before try catch runs

Question

I have this cloud function:

const initCompress = async () => {
  try {
    logger.log('This shows before the function terminated');
    await mkdirp('../../../xxxxx'); <<<< WHY IS IT NOT WAITING FOR THIS TO COMPLETE?
    logger.log('This shows after the function terminated');
    return { success: true };
  } catch (err) {
    ...
  } finally {
    ...
  }
};
export default initCompress;

It is executed via:

const main = async () => {
  exports.compressImage = functions.https.onCall((data, context) => {
    initCompress(data, context);
  });
}

The console log shows:

functions: Beginning execution of "compressImage"
>  {"severity":"INFO","message":"This shows before the function terminated"}
functions: Finished "compressImage" in ~1s
>  {"severity":"INFO","message":"This shows after the function terminated"}

I'm probably doing something silly, but what? Do I need to await something somewhere?

Show us the logger, because if the logger, internally, uses promises (to prevent slowing down the main thread), it would actually show after the main promise would finish. — Akxe, May 11 '21 at 18:51
What exactly is unexpected/wrong with your console output? And what is `compressImage` - you haven't shown that code? What is logging these lines that begin with `functions: …`? — Bergi, May 11 '21 at 18:52
@Bergi `compressImage` is a cloud function. I expected the logs to show before the function terminated. — Ben, May 11 '21 at 18:54
@Ben And what does `compressImage` have to do with `modifyImage`? — Bergi, May 11 '21 at 19:00
@Bergi `compressImage` executes `modifyImage`. I'll update my question to clarify. — Ben, May 11 '21 at 19:02
@Ben Neither `initCompress` nor the `onCall` callback do `return` the promise, so `compressImage` won't know what to wait for. I would recommend to avoid mixing `.then()` syntax with `async`/`await`. [Drop the pointless `.then((response) => { return response; })`](https://stackoverflow.com/q/41089122/1048572). — Bergi, May 11 '21 at 19:16
@Bergi please have a look at the updated question. I simplified the code. Dropped the then catch. Still not able to get `initCompress` to wait for `mkdirp` — Ben, May 11 '21 at 20:30
@Ben The function passed to `functions.https.onCall` still doesn't return anything to wait for. — Bergi, May 11 '21 at 22:43

score 1 · Accepted Answer · answered May 11 '21 at 19:08

1

What you observe is totally normal. By declaring a function as async, your make it return a Promise. That Promise is being returned immediately (it just doesn't resolve immediately). Your code is equivalent of this:

const mkdirp = () => Promise.resolve();
const logger = console;

const modifyImage = () => {
  logger.log('This shows before the function terminated');
  return mkdirp('../../../xxxxx')
    .then(() => logger.log('This shows after the function terminated'))
    .then(() => ({ success: true }))
    .catch(logger.error);
};

modifyImage().then(logger.log);
logger.log('Function finished');

As a conclusion, never forget that async/await is just syntaxic sugar over Promises

answered May 11 '21 at 19:08

Guerric P

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I understand that mkdirp is an async function, so I guess my question is how to contain async functions inside a main function that only terminates once all async functions in it completed. I need to let the client know when it all finished, or when something failed. For now, I can only inform the function fired. – Ben May 11 '21 at 19:56
As you are using an asynchronous function, your "client" has to handle asynchronism either with a callback or with a promise. What is it exactly? – Guerric P May 11 '21 at 20:06
I simplified my async function even more. Please have a look at my question I tried everything - try catch, only then and catch. I am unable to execute initCompress and wait for the final response. – Ben May 11 '21 at 20:29
2

Have you tried to simply `return initCompress(data, context);`? Firebase's `functions.https.onCall` accepts `Promise` as return value – Guerric P May 11 '21 at 20:40
1

Yes. That's was it. I knew it was something silly that I did. Thank you! – Ben May 11 '21 at 20:43

async resolves before try catch runs

1 Answers1