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PromiseConstructor (interface)​

interface PromiseConstructor {
  map<T, U>(
    inputs: Iterable<T | Promise<T>> | AsyncIterable<T | Promise<T>>,
    mapper: (input: T, index: number, length: number) => Promise<U>,
    {
      concurrency,
    }?: {
      concurrency?: number;
    },
  ): Promise<Array<U>>;
}

PromiseConstructor.map (method)​

Like Promise.all, but instead of running everything at once, it'll only run a few Promises at a time (you can choose how many to run at once). It's inspired by Bluebird's Promise.map function.

To use it, you pass in an iterable (array, set, generator function, etc) of inputs and a mapper function that transforms each input into a Promise. You can also optionally specify the maximum number of Promises to wait on at a time by passing an object with a concurrency property, which is a number. The concurrency defaults to 8.

When using an iterable, if the iterable yields a Promise (ie. iterable.next() returns { done: false, value: Promise }), then the yielded Promise will be awaited before being passed into your mapper function. Additionally, async iterables are supported; if iterable.next() returns a Promise, it will be awaited.

map<T, U>(inputs: Iterable<T | Promise<T>> | AsyncIterable<T | Promise<T>>, mapper: (input: T, index: number, length: number) => Promise<U>, {
  concurrency
}?: {
  concurrency?: number;
}): Promise<Array<U>>;