Javascript Nodejs async execution with waterfall method

async-waterfall.js

/*
  With async.waterfall the functions are executed one after the other and the result of each one is used
  to call the next function.
  fn0 -> fn1(resultFromfn0, callback) -> fn2(resultFromfn1, callback) -> fn3(resultFromfn2, callback)
*/
	var async = require("async");

	function fn0(myParam, callback) {
		setTimeout(function(){
			if (myParam === "ciao") {
				callback(null, myParam + " xxxx");
			} else {
				callback("error 123", null);
			}
		}, 400);
		
	}
	
    function fn1(paramFromPreviousFn, callback) {
        setTimeout(function(){
        	console.log("I'm fn1 and you called me with " + paramFromPreviousFn);
        	var ret = paramFromPreviousFn + ' (processed by fn1)';
        	callback(null, ret); // err, result
        }, 350);
    }
	
    function fn2(customParam, paramFromPreviousFn, callback){
        setTimeout(function(){
        	console.log("I'm fn2 and you called me with " + customParam + " + " + paramFromPreviousFn);
        	var ret = paramFromPreviousFn + ' (processed by fn2)';
        	callback(null, ret); // err, result
        }, 100);
    }

	// example with and without custom params
	async.waterfall([fn0.bind(null, "ciao"), fn1, fn2.bind(null, "hello")], function(err, result) {
		console.log("final result = " + result);
		console.log(err);
	});