Async function works with a callback does not work with await

Question

I am trying to integrate into my code an async library function. It works fine as:

client.checkPermission(checkPermissionRequest, (err, response) => {
  if (err || response?.permissionship !== HAS_PERMISSION) {
    const e = err || new Error('You do not have access to event:', id);
    res.code(404).send({ error: e });
  }
});

I want to rewrite it in an "await form" and this does not work. I have been trying:

const response = await client.checkPermission(checkPermissionRequest);

When I run the await code, it fails with: Error: Incorrect arguments passed.

Why could this be happening and how could I fix this?

score 1 · Accepted Answer · answered Sep 13 '22 at 04:08

await doesn't magically make a callback-based API return a promise.

You can however, wrap the call in a promise:

const response = await new Promise((resolve, reject) => {
    client.checkPermission(checkPermissionRequest, (err, response) => {
        if (err) return reject(err);

        return resolve(response);
    });
});

This is called "promisification". If you're a little confused as to how resolve and reject work, maybe the examples in MDN could help with that.

traktor · Answer 2 · 2022-09-13T22:58:27.310

In Node environments you can use the node utility util.promisify to convert the calling conventions of a node style function taking an (error, value) callback as their last argument, into a function that returns a promise without taking a callback argument:

  const util = require('node:util');  //   **OR**
  import {promisify} from 'node:util';

  client.checkPermission = util.promisify( client.checkPermission)

And then call with

  const response = await client.checkPermission(checkPermissionRequest);

Core module imports

 import {promisify} from 'node:util';

imports the promisify utility in a script module. From the docs

Core modules provide named exports of their public API. A default export is also provided which is the value of the CommonJS exports

Async function works with a callback does not work with await

2 Answers2