JavaScript, return function callback in a async function

Question

Is there any kind of performance problem by returning a callback function in a async function as this code?:

import middy from '@middy/core';
import someFunction from 'someFunction';

async function testFunction (
  args,
  callback
) {
  // code
  const data = await someFunction();

  return callback(null, {
    statusCode: 200,
    body: JSON.stringify(data)
  });
}

export const handler = middy(testFunction);

I'm using Middy library, I don't think it's relevant to say but just in case.

You are not returning a callback function, you are executing a function named callback and returning its return value. Also, async is unneeded as you do not await. — crashmstr
– crashmstr, Commented Nov 13, 2020 at 22:04
"Middy allows you to return promises or throw errors from your handlers (instead of calling callback()) and middlewares (instead of calling next())." - that means you should use either. Not both. A function returning a promise with the result should never call a callback with that result. — Bergi
– Bergi, Commented Nov 13, 2020 at 22:09
@crashmstr you are right. I edited the question (I actually need async) — pmiranda
– pmiranda, Commented Nov 13, 2020 at 22:11
@Bergi that's what was I thinking (or something), I'm not sure how should I proceed — pmiranda
– pmiranda, Commented Nov 13, 2020 at 22:12

Vinay Sharma · Accepted Answer · 2021-01-18 07:44:36Z

1

You can return a promise or use callback.

const testFunction = async (event, context) => {
  // ... other logic
  return {
    statusCode: 200,
    body: JSON.stringify(data)
  }
}

This is a common pain point with new comers to middy. This has been addressed in middy v2 with the deprecation of callbacks altogether.

edited Jan 18, 2021 at 7:44

Vinay Sharma

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answered Jan 18, 2021 at 7:36

will Farrell

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2 Comments

pmiranda Over a year ago

middy v2? ahh good, that's pretty new github.com/middyjs/middy/tree/release/2.x

will Farrell Over a year ago

I wrote it over the holidays. I hope to have an alpha out this month.

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