promises.js

readFile("filename.txt", function(err, data) {
	console.log("5 seconds have elapsed");
	if (err) { return; }
	readFile("otherfile.txt", function(err, data) {
		console.log("10 seconds have elapsed");
		if (err) { return; }
		writeFileToNetwork(data, function(err, response) {
			if (err) { return; }
			console.log("complete");
		});
	});
});

readFile("otherfile.txt", function(err, data) {
	console.log(data);
});



readFile("filename.txt")
.then(function (data) {
	console.log(data);
	return readFile("otherfile.txt");
})
.then(function (otherData) {
	console.log(otherData);
	return writeFileToNetwork(otherData);
})
.then(function (response) {
	console.log("complete");
})
.catch(function (err) {
	console.error(err);
});



// var data = readFile("filename.txt");       - 5 secs
// var otherFile = readFile("otherfile.txt"); - 5 secs