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
}

With typescript types / es6 module syntax:

async function asyncFlatMap<T, O>(arr: T[], asyncFn: (t: T) => Promise<O[]>): Promise<O[]> {
    return Promise.all(flatten(await asyncMap(arr, asyncFn)))
}

function flatMap<T, O>(arr: T[], fn: (t: T) => O[]): O[] {
    return flatten(arr.map(fn))
}

function asyncMap<T, O>(arr: T[], asyncFn: (t: T) => Promise<O>): Promise<O[]> {
    return Promise.all(arr.map(asyncFn))
}

function flatten<T>(arr: T[][]): T[] {
    return ([] as T[]).concat(...arr);
}

export {
    asyncFlatMap,
    asyncMap,
    flatMap,
    flatten
}

should you not flat first and then map? Your map executes on both single elements and arrays of elements.

@peveuve If you want flat first you don't need a function. You could write flatten(arr).map(fn).
Actually, this gist is a little bit obsolete because now we have official flatMap and flat