@root/async-router

A lightweight, zero-dependency JavaScript library to bring native Promises and
async/await to Express.


Wraps the Express Router and provides a drop-in replacement to allow you to
progressively enhance your routes with Promise and await support.

``js
// Handle Async & Promise routes - and normal routes too!
app.get('/foo', async function (req, res) {
// no more try/catch wrappers
// no more 'unhandledRejection' errors
let user = await UserService.findById(req.user.id);

res.json(user);
});
`

Features

- [x] API-compatible with express.Router()
- [x] NO refactoring required!
- [x] supports Promises
- [x] supports async/await
- [x] Proper error handling!
- [x] No more unhandledPromiseRejectionWarning
- [x] No more unhandledRejection
- [x] No uncaught exception server crashes
- [x] res.json() _can_ be called automatically

Usage

$3

Swap out app for the async router, and handle the server separately:

`js
let app = require('@root/async-router').Router();

// ...

let server = express().use('/', app);
http.createServer(server).listen(3000, onListen);
`

Keep existing routes just the (ugly) way they are...

`js
// yuck!
app.get('/profile', async function (req, res, next) {
try {
let results = await ProfileModel.get(req.user.id);
res.json(results);
} catch (e) {
return next(e);
}
});
`

Or delete the cruft to give them a facelift:

`js
// yay!
app.get('/profile', async function (req, res) {
let profile = await ProfileModel.get(req.user.id);
res.json(profile);
});
`

#### Caveats

If you need to set express options, you'll move that down to the bottom as well:

`js
let app = require('@root/async-router').Router();

// ...

let server = express().use('trust proxy', 1).use('view engine', 'pug').use('/', app);
http.createServer(server).listen(3000, onListen);
`

Also, if you do happen to have a few routes that explicitly
res.json() in a callback after having returning a value,
those would need to be updated - a very rare case, but I'm
sure it exists in some code somewhere.

$3

`js
'use strict';

let http = require('http');
let express = require('express');
let app = require('@root/async-router').Router();

// Handle Async & Promise routes
app.get('/foo', async function (req, res) {
let user = await UserService.findById();
if (!user) {
throw new Error('User not found');
}

// Note: if you return a value,
// res.json() will be called automatically
// (however, just because you can doesn't mean you should)
return user;
});

// Handles existing routes too - no refactoring required!
app.get('/foo', async function (req, res) {
try {
let user = await UserService.findById();
} catch (e) {
console.error('Unexpected');
console.error(e);
res.statusCode = 500;
res.end('Internal Server Error');
}

if (!user) {
res.statusCode = 404;
res.json({ error: 'User not found' });
return;
}

res.json(user);
});

// Handle errors (must come after associated routes)
app.use('/', function (err, req, res, next) {
console.error('Unhandled Error');
console.error(err);
res.statusCode = 500;
res.end(err.message);
});

// Start node.js express server
let server = express().use('/', app);
http.createServer(server).listen(3000, function () {
console.info('Listening on', this.address());
});
`

Also, since it's useful to have this snippet for demos:

`js
async function sleep(ms) {
await new Promise(function (resolve) {
setTimeout(resolve, ms);
});
}
`

API

$3

`js
let app = require('@root/async-router').Router();
`

This is just a wrapper around express.Router(), which is what provides the
default router and "mini apps" of express - so it has all of the same methods
and function signatures:

`js
app.use(path, middlewares);
app.route(path, minApp);
app.head(path, fns);
app.get(path, fns);
app.post(path, fns);
app.patch(path, fns);
app.delete(path, fns);
// ... etc
`

Any incompatibility should be file as a bug.

$3

It does NOT copy the top-level express server API. You should still use express for that:

`js
// top-level options are still handled by the express server instance
let server = express().set('trust proxy', 1).set('view engine', 'pug').use('/', app);

require('http').createServer(server).listen(3000, onListen);

function onListen() {
console.info('Listening on', this.address());
}
`

$3

The wrap(app) is the best way to add async/await
support to your Express app or Router.

`js
let syncApp = express.Router();
let app = require('@root/async-router').wrap(syncApp);
`

Alternatives

If you'd like to go dependency-free and use vanilla Express.js as-is,
your best options are probably:

1. Use a wrapper promise _in_ each Handler
`js
app.use(function (req, res, next) {
async function h() {
let result = await DB.doStuff();
res.json(result);
}
Promise.resolve().then(h).catch(next);
});
`
2. Wrap _around_ each handler

`js
app.use(
nextify(async function (req, res, next) {
let result = await DB.doStuff();
res.json(result);
})
);

function nextify(fn) {
return function (req, res, next) {
async function h() {
await fn(req, res, next);
}
Promise.resolve().then(h).catch(next);
};
}
`

LICENSE

Fork of [express-promisify-router`][fork] to [bugfix error handling][fix].

[fork]: https://github.com/michal-choluj/express-promisify-router#readme
[fix]: https://github.com/michal-choluj/express-promisify-router/pull/3

MIT License

See LICENSE.