javascript - Is it an anti-pattern to use async/await inside of a new Promise() constructor?

Question

I'm using the async.eachLimit function to control the maximum number of operations at a time.

const { eachLimit } = require("async");

function myFunction() {
 return new Promise(async (resolve, reject) => {
   eachLimit((await getAsyncArray), 500, (item, callback) => {
     // do other things that use native promises.
   }, (error) => {
     if (error) return reject(error);
     // resolve here passing the next value.
   });
 });
}

As you can see, I can't declare the myFunction function as async because I don't have access to the value inside the second callback of the eachLimit function.

Answer 1

You're effectively using promises inside the promise constructor executor function, so this the Promise constructor anti-pattern.

Your code is a good example of the main risk: not propagating all errors safely. Read why there.

In addition, the use of async/await can make the same traps even more surprising. Compare:

let p = new Promise(resolve => {
  ""(); // TypeError
  resolve();
});

(async () => {
  await p;
})().catch(e => console.log("Caught: " + e)); // Catches it.