Promise constructors take an executor function as an argument with resolve and reject parameters that can be used to control the state of the created Promise. This function is allowed to be async but this is generally not a good idea for several reasons:

• If an async executor function throws an error, the error will be lost and won't cause the newly-constructed Promise to reject. This could make it difficult to debug and handle some errors.
• If an async Promise executor function is using await, then this is usually a sign that it is not actually necessary to use the new Promise constructor and the code can be restructured to avoid the use of a promise, or the scope of the new Promise constructor can be reduced, extracting the async code and changing it to be synchronous.

Invalid:

new Promise(async function (resolve, reject) {});
new Promise(async (resolve, reject) => {});

Valid:

new Promise(function (resolve, reject) {});
new Promise((resolve, reject) => {});