@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.

// 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

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

Usage

TL;DR

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

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...

// 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:

// 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:

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.

Full Example

'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:

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

API

Router() - same as express.Router()

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:

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.

NOT an express server

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

// 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());
}

wrap(app)

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

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

   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

   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 to bugfix error handling.

MIT License

See LICENSE.