Promises com Q

com_q.js

	// promises
	var q = require("q")

	var fs = require('fs');
	var filename = "dados.txt";

	function lerDados(filename){
		var defer = q.defer();
		fs.readFile(filename, 'utf8', function(err, data) {
			//defer.resolve(data);
			defer.reject(data);
		});
		return defer.promise;
	}
	function gravarBD(data){
		var defer = q.defer();
		fs.writeFile("dados1.txt", data+" 1", function(err) {
			defer.resolve(data);
		});
		return defer.promise;
	}
	function gerarLog(data){
		var defer = q.defer();
		fs.writeFile("dados2.txt", data+" 2", function(err) {
			defer.resolve(data);
		});
		return defer.promise;    
	}

	lerDados(filename)
	.then(gravarBD)
	.then(gerarLog)
	.then(function(data){
		console.log("Processo finalizado");
	}, function(err){
		console.log("erro "+err);
	});

sem_promises.js

	var fs = require('fs');
	var filename = "dados.txt";

	fs.readFile(filename, 'utf8', function(err, data) {
	  fs.writeFile("dados1.txt", data+" 1", function(err) {
		fs.writeFile("dados2.txt", data+" 2", function(err) {
			console.log("Processo terminado");
		});     
	  }); 
	});