Using async function within synchronous code

Question

I'm using a library called sqs-consumer to process SQS messages. The library is expecting the message handler to look like:

handleMessage: (message, done) => {
 // do some work with `message`
 done();
}

On the other hand though I have async code

async function sendEmail() {
 return await ...
}

Is there a good way to run the sendEmail within handleMessage, wait for it to finish, and then to call done?

• lucascaro: Possible duplicate of async/await implicitly returns promise?
• CertainPerformance: Note that return await is pretty pointless if that's the only await you're using in the function - just use a standard function instead, and you can simply return the plain Promise

Answer 1

You can use your promise-based code inside a callback like this:

handleMessage: (message, done) => {
 // do some work with `message`
 sendEmail().then(done).catch(...);
}

In some cases, you could also make a new method for handleMessage() that actually expects a promise to be returned and works with that promise directly rather than using a plain callback at all.

---

Also, not that there is no point to using return await ... at the end of your function. You can just return the promise directly:

So, instead of:

async function sendEmail() {
 // other code here
 return await someFuncThatReturnsPromise();
}

You can just do:

async function sendEmail() {
 // other code here
 return someFuncThatReturnsPromise();
}

That extra await adds no value or utility.

Answer 2

As long as the library doesn't care what you return from handleMessage you can also use async/await in the handlerMessage function directly:

handleMessage: async (message, done) => {
 await sendEmail();
 done();
}