Promisified, asynchronous ES6 for..of

Installation

npm install async-for-of

Usage

async-for-of can loop asynchronously over any iterable, only requesting the item when "next" is called

var forOf = require('async-for-of')

forOf(iterable, (item, next, end) => { 
  //do something with item, then call next() or end(result)
}).then((result) => {
  //do something with the result
})

iterable is an array, generator, function or custom iterable of any type (typically Promises)

forOf returns a Promise that is fulfilled when:

• end is called (with resolve with the value passed to that function)
• the iterable returns done (will resolve with an undefined result)

Check out the tests to see expected behaviour.

##Examples

Asynchronous Random Number Generator

This example asynchronously generates random numbers and resolves when the result matches certain criteria

var asyncRandomGenerator = () => {
  console.log('Generating value')
  return Promise.resolve(Math.random())
}

forOf(asyncRandomGenerator, (item, next, end) => {
  item.then(val => {
    console.log('Inspecting value')
    if (val < 0.1)
      end(val)
    else
      next()
  })
}).then(val => console.log('Success: ' + val))

Asynchronous Random Number Generator #2

This builds on the above example, using an ES6 generator to add some control flow - in this case, enforcing the maximum number of attempts

var asyncRandomGenerator = function*() {
  var maxAttempts = 5
  for (var i = 0; i < maxAttempts; i++) {
    console.log('Generating value')
    yield Promise.resolve(Math.random())
  }
  throw 'Max Attempts Exceeded'
}

forOf(asyncRandomGenerator(), (promise, next, end) => {
  promise.then(val => {
    console.log('Inspecting value')
    if (val < 0.1)
      end(val)
    else
      next()
    });
}).then(val => console.log('Success: ' + val))
.catch(err => console.log('Failure: ' + err))

Peer Discovery

This example finds an active peer from a list (ideally broadcasted) and resolves with a socket

var server = net.createServer();
server.listen(8002);

var peers = [
  { host: '127.0.0.1', port: 8000 },
  { host: '127.0.0.1', port: 8001 },
  { host: '127.0.0.1', port: 8002 }
]

forOf(peers, (peer, next, end) => {
  console.log('Attempting to connect to ' + JSON.stringify(peer))

  var socket = net.connect(peer.port, peer.host)
  socket.on('connect', () => end({ peer, socket }))
  socket.on('error', next)
}).then(result => {
  console.log('Peer found: ' + JSON.stringify(result.peer))
  
  //do something with result.socket
})