no-async-promise-executor.md

Pattern: Use of async function as Promise executor

Issue: -

Description

The new Promise constructor accepts an executor function that controls the state of the created Promise through resolve and reject parameters. While the executor can be an async function, this is usually a mistake because:

• If an async executor function throws an error, the error will be lost and won't cause the newly-constructed Promise to reject
• Use of await in a Promise executor usually indicates that the new Promise constructor is unnecessary or its scope can be reduced

Examples

Example of incorrect code:

const result = new Promise(async function executor(resolve, reject) {
  const result = await readFile("foo.txt");
  resolve(result);
});

The above code is problematic because any errors thrown during the async execution will be lost and the Promise won't reject properly.