gistfile1.js

var async = require('async');

function one(cb) {
    console.log("one");
    cb();
}

function two(cb) {
    function three(callback){
        var a = [];
        for (var i = 1; i <= 3; i++) {
            a.push(i);
        };
        callback(null, a);
    }

    function four(work, callback) {
        console.log(work);
        callback(null);
    }

    async.waterfall([three, four], cb); // A cb is required by the series to proceed to the outer three(). 
                                        // If cb was outside the waterfall, it would have been called too early.
}

function three(cb) {
    console.log('even more');
    cb();
}

async.series([one, two, three]);