Using Express.js with Promises

promise-router.js

/* Without using express-promise-router...
 * If either of the two Promise-returning methods ends up failing (ie. rejecting),
 * an uncaught exception will be printed to stdout, and the client will never get
 * a response - instead, they'll be stuck on an infinitely loading page.
 */

express = require("express").router();

router.get("/", function(req, res) {
	Promise.try(function(){
		return doSomethingThatReturnsAPromise();
	}).then(function(result){
		return doSomethingElsePromisey(result);
	}).then(function(otherResult){
		res.send("The result was " + otherResult);
	});
});


/* Using express-promise-router...
 * If either of the two Promise-returning methods ends up failing (ie. rejecting),
 * the error will be caught transparently by the router, and it will be passed down
 * through the regular Express error handling process; that is, passed on to the
 * error-handling middleware you have specified.
 * Note how it now *returns* the Promise - this is required.
 */

express = require("express-promise-router");

router.get("/", function(req, res) {
	return Promise.try(function(){
		return doSomethingThatReturnsAPromise();
	}).then(function(result){
		return doSomethingElsePromisey(result);
	}).then(function(otherResult){
		res.send("The result was " + otherResult);
	});
});