functions and patterns for asynchronous code - Node.js

 Async is a utility module which provides straight-forward, powerful
 functions for working with asynchronous Javascript.
 .
 Async provides around 20 functions that include the usual 'functional'
 suspects (map, reduce, filter, forEach…) as well as some common
 patterns for asynchronous control flow (parallel, series, waterfall…).
 All these functions assume you follow the Node convention of providing
 a single callback as the last argument of your async function.
 .
 This provides async for use with Node.js -
 an event-based server-side JavaScript engine.