Async forEach

forEachAsync.js

function forEach(array, fn, cb){
  var i = -1
  function next(err){
    if (err) return cb&&cb(err)
    i += 1
    if (i<array.length){
      fn(array[i], next, i)
    } else {
      cb&&cb(null)
    }
  }
  next()
}