return a flatten map resolved by async function

async-flat-map.js

async function asyncFlatMap (arr, asyncFn) {
    return Promise.all(flatten(await asyncMap(arr, asyncFn)))
}

function asyncMap (arr, asyncFn) {
    return Promise.all(arr.map(asyncFn))
}

function flatMap (arr, fn) {
    return flatten(arr.map(fn))
}

function flatten (arr) {
    return [].concat(...arr)
}

module.exports = {
    asyncFlatMap,
    asyncMap,
    flatMap,
    flatten
}

I guess asyncFlatMap() is still convenient to have. Modern definition (hat tip to Gemini AI):

async function asyncFlatMap<T, O>(arr: T[], asyncFn: (t: T) => Promise<O[]>): Promise<O[]> {
    const promises = arr.map(asyncFn);
    const nestedArray = await Promise.all(promises);
    return nestedArray.flat();
}