promise-map-first

Get the value of the first promise in a series to resolve

Runs a series of promises sequentially while iterating through a value, ignoring rejections, and returns the value of the first promise in the series to resolve.

Use this like an asynchronous for loop, where the condition is a Promise's resolve/reject mechanism.

Installation

npm install promise-map-first

Usage

const first = require('promise-map-first');
const pify = require('pify');
const readFile = pify(require('fs').readFile);

const files = [
  'one.jpg',
  'two.txt', // <-- this file exists
  'three.mov', // <-- this file also exists
];

first(files, file => readFile(file)).then(res => {
  // res.index is 1
  // res.value is the contents of two.txt
});

API

first(input, fn)

Iterate over input by calling fn for each item in the series. The function should return a promise. Each promise is called sequentially. If a promise rejects, the next one is called. If a promise resolves, the value is returned, and no further functions are called.

• input (Iterable): items to iterate through.
• fn (Function): iterating function. Should return a promise. Takes these parameters:
  • value: value of current item.
  • index (Integer): index of current item.
  • array (Iterable): collection being iterated through.

Returns a Promise which resolves as soon as a promise in the series resolves. The promise contains an object with these properties:

• index (Integer): index of the item being referenced when the first promise resolved.
• value: value contained in the first resolved promise.

Local Development

git clone https://github.com/spacedoc/promise-map-first
cd promise-map-first
npm install
npm test

License

MIT © Geoff Kimball