Is Using `async/await` Inside a `Promise` Constructor an Anti-Pattern?

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

Asynchronous programming can be challenging, especially when dealing with nested callbacks. To simplify this, ES6 introduced the async/await syntax. However, when using async/await within the constructor function of a new Promise(), caution is needed.

In the example provided:

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.
  });
});

You're using await to call getAsyncArray, which returns a Promise, but within the Promise constructor's executor function. This is known as the "Promise constructor anti-pattern."

The primary danger with this pattern is that errors might not be handled properly. Asynchronicity can create unpredictable behavior, and utilizing async/await makes it harder to see potential issues.

For instance, a typo in the getAsyncArray function would lead to a TypeError, but it might not be caught by the eachLimit callback's error handling. However, if async/await were removed, the error would be thrown outside of the Promise constructor and handled appropriately.

In conclusion, while using async/await within the constructor function of a Promise() may seem convenient, it's an anti-pattern due to the potential for error handling issues. Instead, consider using async/await outside of the Promise constructor to ensure proper error propagation and code maintainability.

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