callback vs async

async.js

var request = require('request');
var cheerio = require('cheerio');
var async   = require('async');
var jar     = request.jar();
var form;

async.waterfall([
    function(callback){
        request({
            url    : 'https://github.com/login',
            method : 'GET',
            jar    : jar
        }, function(err, res, body) {

            console.log('get login page first')

            callback(err, res, body);
        })
    },
    function(res, body, callback){

        console.log('then get authenticity_token')

        var $ = cheerio.load(res.body);
        if(res.statusCode === 200) {
            form  = {
                utf8               : true,
                authenticity_token : $('input[name="authenticity_token"]').val()
            };
            form.login    = 'YOUR_EMAIL_ADRESS';
            form.password = 'YOUR_PASSWORD';

            request({
                url    : 'https://github.com/session',
                method : 'POST',
                jar    : jar,
                form   : form
            }, function(err, res, body) {
                callback(err, res, body);
            })
        }
    },
    function(res, body, callback){

        console.log('success login and redirect to /login')

        if(res.statusCode === 302) {
            request({
                url    : 'https://github.com/login',
                method : 'GET',
                jar    : jar
            }, function(err, res, body) {
                callback(err, res, body)
            })
        }
    }
],
function(err, res, body){
    if (res.statusCode === 200) {
        var $ = cheerio.load(res.body);
        console.log('user: ',$('span.css-truncate-target').eq(0).text());
    }
});

callback.js

var request = require('request');
var cheerio = require('cheerio');
var jar     = request.jar();
var form;

console.log('get login page first')

request({
    url    : 'https://github.com/login',
    method : 'GET',
    jar    : jar
}, function(err, res, body) {

    console.log('then get authenticity_token')

    if (res.statusCode === 200) {
        var $ = cheerio.load(res.body);
        form  = {
            utf8               : true,
            authenticity_token : $('input[name="authenticity_token"]').val()
        };
        form.login    = 'YOUR_EMAIL_ADRESS';
        form.password = 'YOUR_PASSWORD';
        request({
            url    : 'https://github.com/session',
            method : 'POST',
            form   : form,
            jar    : jar
        }, function(err, res, body) {

            console.log('success login and redirect to /login')

            if (res.statusCode === 302) {
                request({
                    url    : 'https://github.com/login',
                    method : 'GET',
                    jar    : jar
                }, function(err, res, body) {
                    if (res.statusCode === 200) {
                        var $ = cheerio.load(res.body);
                        console.log('user: ',$('span.css-truncate-target').eq(0).text());
                    }
                });
            }
        })
    }
});