Catching errors from nested async/await functions

Question

I have a function chain in a node 4.3 script that looks something like, callback -> promise -> async/await -> async/await -> async/await

like so:

const topLevel = (resolve, reject) => {
    const foo = doThing(data)
    .then(results => {
        resolve(results)
    })
    .catch(err => {
        reject(err)
    })
}

async function doThing(data) {
    const thing = await doAnotherThing(data)
    return thing
}

async function doAnotherThing(data) {
    const thingDone = await etcFunction(data)
    return thingDone
}

(The reason it isn't async/await all the way through is that the top level function is a task queue library, and ostensibly can't be run async/await style)

If etcFunction() throws, does the error bubble up all the way to the top-level Promise?

If not, how can I bubble-up errors? Do I need to wrap each await in a try/catch and throw from there, like so?

async function doAnotherThing(data) {
   try {
     await etcFunction(data)
   } catch(err) {
     throw err  
   }
}

"the top level function is a task queue library, and ostensibly can't be run async/await style" - there's no reason why a queue library couldn't use async functions as tasks. You really shouldn't have to deal with callbacks. If you need to use a particular queue library that employs callback style, use a wrapper function. — Bergi
– Bergi, Commented Nov 28, 2016 at 16:53
@Bergi makePromise is actually an async function, but since it's called from a non-async environment, i'm handling it like a promise. re: i agree, I'm going to try and promise-ify it eventually, but can I have reliable error bubbling in the mean time? — Brandon
– Brandon, Commented Nov 28, 2016 at 16:58
@Bergi i removed the makePromise bit from the snippet to clarify--the first function called in the top-level is an async function i'm treating as a regular Promise — Brandon
– Brandon, Commented Nov 28, 2016 at 17:00
@Bergi yes, thanks for catching that & the other errors- i should've just copied the actual code instead of trying to recreate in pseudocode — Brandon
– Brandon, Commented Nov 28, 2016 at 17:04

Community · Accepted Answer · 2017-05-23 12:30:29Z

If etcFunction() throws, does the error bubble up all the way through the async functions?

Yes. The promise returned by the outermost function will be rejected. There's no need to do try { … } catch(e) { throw e; }, that's just as pointless as it would be in synchronous code.

… bubble up all the way to the top-level Promise?

No. Your topLevel contains multiple mistakes. If you don't return the doThing(data) from the then callback, it will be ignored (not even awaited) and the rejection stays unhandled. You'll have to use

.then(data => { return doThing(data); })
// or
.then(data => doThing(data))
// or just
.then(doThing) // recommended

And in general, your function should look like this:

function toplevel(onsuccess, onerror) {
    makePromise()
    .then(doThing)
    .then(onsuccess, onerror);
}

No unnecessary function expressions, no .then(…).catch(…) antipattern (that could lead to onsuccess and onerror to both be called).

Clifton Labrum · Accepted Answer · 2019-06-02 04:07:31Z

0

I know this question is old, but as your question is written, wouldn't the doAnotherThing() function be unnecessary because it just wraps etcFunction()?

So your code could be simplified to this:

async function topLevel(){
  let thing = await doThing(data)
  let thingDone = await etcFunction(data)
  //Everything is done here...
}

//Everything starts here...
topLevel()

answered Jun 2, 2019 at 4:07

Clifton Labrum

14.3k13 gold badges81 silver badges160 bronze badges

1 Comment

Nick Bull Over a year ago

I think this is mock code to demonstrate nested await calls

Dharman · Accepted Answer · 2021-03-07 19:39:43Z

0

I just had a similar issue where my nested errors didn't appear to bubble up to my top level function.

The fix for me was to remove the "try / catch" from my nested function and allow the error to just be thrown.

edited Mar 7, 2021 at 19:39

Dharman♦

33.9k27 gold badges105 silver badges157 bronze badges

answered Mar 7, 2021 at 19:34

nowlena

1511 gold badge3 silver badges9 bronze badges

Collectives™ on Stack Overflow

Catching errors from nested async/await functions

3 Answers 3

Comments

1 Comment

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

Comments

1 Comment

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related