@root/async-router
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Write Express middleware and route handlers using async/await
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# [@root/async-router](https://github.com/therootcompany/async-router)
A lightweight, zero-dependency JavaScript library to bring native `Promise`s and
`async`/`await` to Express.
[](https://www.youtube.com/watch?v=XFn0SJmGYs4&list=PLxki0D-ilnqZfyo2dZe11ZNGP7RJxJcoA&index=18)
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 `Promise`s
- [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
### TL;DR
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.
### Full Example
```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
### Router() - same as express.Router()
```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.
### NOT an express server
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());
}
```
### wrap(app)
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](/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](/LICENSE).