Async mapping with continuable

async-map.js

var assert = require('assert')
var setTimeout = require('timers').setTimeout

var list = [1, 2, 3, 4, 5]

var conts = list.map(function (n) {
    return function continuable(cb) {
        setTimeout(function () {
            cb(null, n * 2)
        }, 10)
    }
})

var answer = list(conts)(function (err, results) {
    assert.deepEqual(results, [2, 4, 6, 8, 10])
})

// https://gist.github.com/Raynos/5486205
//  lists := (tasks:Array<Continuable<T>>)
//      => Continuable<Array<T>>
function list(tasks) {
    return function continuable(callback) {
        var result = []
        var ended = false
        var count = 0
        var length = tasks.length

        tasks.forEach(function (source, index) {
            source(function (err, value) {
                if (err && !ended) {
                    callback(err)
                } else if (!err) {
                    result[index] = value
                    if (++count === length) {
                        callback(null, result)
                    }
                }
            })
        })
    }
}