µExpress / Ultimate Express

The Ultimate Express. Fastest http server with full Express compatibility, based on µWebSockets.

This library is a very fast re-implementation of Express.js 4. It is designed to be a drop-in replacement for Express.js, with the same API and functionality, while being much faster. It is not a fork of Express.js.
To make sure µExpress matches behavior of Express in all cases, we run all tests with Express first, and then with µExpress and compare results to make sure they match.

npm install ultimate-express -> replace express with ultimate-express -> done*

Use npm install ultimate-express@node-v18 to install last version that supported Node.js v18.

Difference from similar projects

Similar projects based on uWebSockets:

• express on Bun - since Bun uses uWS for its HTTP module, Express is about 2-3 times faster than on Node.js, but still almost 2 times slower than µExpress because it doesn't do uWS-specific optimizations.
• hyper-express - while having a similar API to Express, it's very far from being a drop-in replacement, and implements most of the functionality differently. This creates a lot of random quirks and issues, making the switch quite difficult. Built in middlewares are also very different, middlewares for Express are mostly not supported.
• uwebsockets-express - this library is closer to being a drop-in replacement, but misses a lot of APIs, depends on Express by calling it's methods under the hood and doesn't try to optimize routing by using native uWS router.

Performance

Test results

Tested using wrk (-d 60 -t 1 -c 200). Tested on Ubuntu 22.04, Node.js 20.17.0, AMD Ryzen 5 3600, 64GB RAM.

Test	Express req/sec	µExpress req/sec	Express throughput	µExpress throughput	µExpress speedup
routing/simple-routes (/)	11.16k	75.14k	2.08 MB/sec	14.46 MB/sec	6.73X
routing/lot-of-routes (/999)	4.63k	54.57k	0.84 MB/sec	10.03 MB/sec	11.78X
routing/some-middlewares (/90)	10.12k	61.92k	1.79 MB/sec	11.32 MB/sec	6.12X
routers/nested-routers (/abccc/nested/ddd)	10.18k	51.15k	1.82 MB/sec	9.40 MB/sec	5.02X
middlewares/express-static (/static/index.js)	6.58k	32.45k	10.15 MB/sec	49.43 MB/sec	4.87X
engines/ejs (/test)	5.50k	40.82k	2.45 MB/sec	18.38 MB/sec	7.42X
middlewares/body-urlencoded (/abc)	8.07k	50.52k	1.68 MB/sec	10.78 MB/sec	6.26X
middlewares/compression-file (/small-file)	4.81k	14.92k	386 MB/sec	1.17 GB/sec	3.10X

Performance against other frameworks

Tested using bun-http-framework-benchmark. This table only includes Node.js results. For full table with other runtimes, check here.

Framework	Average	Ping	Query	Body
uws	95,531.277	109,960.35	105,601.47	71,032.01
ultimate-express (declarative)	86,794.997	108,546.44	105,869.75	45,968.8
hyper-express	68,959.92	82,547.21	71,685.51	52,647.04
ultimate-express	60,839.75	68,938.53	66,173.86	47,406.86
h3	35,423.263	41,243.68	34,429.26	30,596.85
fastify	33,094.62	40,147.67	40,076.35	19,059.84
hono	26,576.02	36,215.35	34,656.12	8,856.59
koa	24,045.08	28,202.12	24,590.84	19,342.28
express	10,411.313	11,245.57	10,598.74	9,389.63

Other benchmarks:

• TechEmpower / FrameworkBenchmarks
• the-benchmarker / web-frameworks

Performance on real-world application

Also tested on a real-world application with templates, static files and dynamic pages with data from database, and showed 1.5-4X speedup in requests per second depending on the page.

Differences from Express

In a lot of cases, you can just replace require("express") with require("ultimate-express") and everything works the same. But there are some differences:

• case sensitive routing is enabled by default.
• a new option catch async errors is added. If it's enabled, you don't need to use express-async-errors module.
• request body is only read for POST, PUT and PATCH requests by default. You can add additional methods by setting body methods to array with uppercased methods.
• For HTTPS, instead of doing this:

1const https = require("https");
2const express = require("express");
3
4const app = express();
5
6https.createServer({
7    key: fs.readFileSync('path/to/key.pem'),
8    cert: fs.readFileSync('path/to/cert.pem')
9}, app).listen(3000, () => {
10    console.log('Server is running on port 3000');
11});

You have to pass uwsOptions to the express() constructor:

1const express = require("ultimate-express");
2
3const app = express({
4    uwsOptions: {
5        // https://unetworking.github.io/uWebSockets.js/generated/interfaces/AppOptions.html
6        key_file_name: 'path/to/key.pem',
7        cert_file_name: 'path/to/cert.pem'
8    }
9});
10
11app.listen(3000, () => {
12    console.log('Server is running on port 3000');
13});

• This also applies to non-SSL HTTP too. Do not create http server manually, use app.listen() instead.
• Node.JS max header size is 16384 bytes, while uWebSockets by default is 4096 bytes, so if you need longer headers set the env variable UWS_HTTP_MAX_HEADERS_SIZE to max byte count you need.

Performance tips

1. µExpress tries to optimize routing as much as possible, but it's only possible if:

• case sensitive routing is enabled (it is by default, unlike in normal Express).
• only string paths without regex characters like *, +, (), {}, etc. can be optimized.
• only 1-level deep routers can be optimized.

Optimized routes can be up to 10 times faster than normal routes, as they're using native uWS router and have pre-calculated path.

2. Do not use external serve-static module. Instead use built-in express.static() middleware, which is optimized for uExpress.

3. Do not use body-parser module. Instead use built-in express.text(), express.json() etc.

4. Do not set body methods to read body of requests with GET method or other methods that don't need a body. Reading body makes endpoint about 15% slower.

5. By default, µExpress creates 1 (or 0 if your CPU has only 1 core) child thread to improve performance of reading files. You can change this number by setting threads to a different number in express(), or set to 0 to disable thread pool (express({ threads: 0 })). Threads are shared between all express() instances, with largest threads number being used. Using more threads will not necessarily improve performance. Sometimes not using threads at all is faster, please test both options.

WebSockets

Since you don't create http server manually, you can't properly use http.on("upgrade") to handle WebSockets. To solve this, there's currently 2 options:

• There's a sister library that implements ws compatible API: Ultimate WS. It's same concept as this library, but for WebSockets: fast drop-in replacement for ws module with support for Ultimate Express upgrades. There's a guide for how to upgrade http requests in the documentation.
• You can simply use app.uwsApp to access uWebSockets.js App instance and call its ws() method directly.

HTTP/3

HTTP/3 is supported. To use:

1const app = express({
2  http3: true,
3  uwsOptions: {
4    key_file_name: '/path/to/example.key',
5    cert_file_name: '/path/to/example.crt'
6  }
7});

Compatibility

In general, basically all features and options are supported. Use Express 4.x documentation for API reference.

✅ - Full support (all features and options are supported)
🚧 - Partial support (some options are not supported)
❌ - Not supported

express

• ✅ express()
• ✅ express.Router()
• ✅ express.json()
• ✅ express.urlencoded()
• ✅ express.static()
• ✅ express.text()
• ✅ express.raw()
• 🚧 express.request (this is not a constructor but a prototype for replacing methods)
• 🚧 express.response (this is not a constructor but a prototype for replacing methods)

Application

• ✅ app.listen(port[, host][, callback])
• ✅ app.listen(unix_socket[, callback])
• ✅ app.METHOD() (app.get, app.post, etc.)
• ✅ app.route()
• ✅ app.all()
• ✅ app.use()
• ✅ app.mountpath
• ✅ app.set()
• ✅ app.get()
• ✅ app.enable()
• ✅ app.disable()
• ✅ app.enabled()
• ✅ app.disabled()
• ✅ app.path()
• ✅ app.param(name, callback)
• ✅ app.param(callback)
• ✅ app.engine()
• ✅ app.render()
• ✅ app.locals
• ✅ app.settings
• ✅ app.engines
• ✅ app.on("mount")
• ✅ HEAD method
• ✅ OPTIONS method

Application settings

• ✅ case sensitive routing
• ✅ env
• ✅ etag
• ✅ jsonp callback name
• ✅ json escape
• ✅ json replacer
• ✅ json spaces
• ✅ query parser
• ✅ strict routing
• ✅ subdomain offset
• ✅ trust proxy
• ✅ views
• ✅ view cache
• ✅ view engine
• ✅ x-powered-by

Request

• ✅ implements Readable stream
• ✅ req.app
• ✅ req.baseUrl
• ✅ req.body
• ✅ req.cookies
• ✅ req.fresh
• ✅ req.hostname
• ✅ req.header
• ✅ req.headers
• ✅ req.headersDistinct
• ✅ req.rawHeaders
• ✅ req.ip
• ✅ req.ips
• ✅ req.method
• ✅ req.url
• ✅ req.originalUrl
• ✅ req.params
• ✅ req.path
• ✅ req.protocol
• ✅ req.query
• ✅ req.res
• ✅ req.secure
• ✅ req.signedCookies
• ✅ req.stale
• ✅ req.subdomains
• ✅ req.xhr
• 🚧 req.route (route implementation is different from Express)
• 🚧 req.connection, req.socket (only end(), encrypted, remoteAddress and localPort are supported)
• ✅ req.accepts()
• ✅ req.acceptsCharsets()
• ✅ req.acceptsEncodings()
• ✅ req.acceptsLanguages()
• ✅ req.get()
• ✅ req.is()
• ✅ req.param()
• ✅ req.range()

Response

• ✅ implements Writable stream
• ✅ res.app
• ✅ res.headersSent
• ✅ res.req
• ✅ res.locals
• ✅ res.append()
• ✅ res.attachment()
• ✅ res.cookie()
• ✅ res.clearCookie()
• ✅ res.download()
• ✅ res.end()
• ✅ res.format()
• ✅ res.getHeader(), res.get()
• ✅ res.json()
• ✅ res.jsonp()
• ✅ res.links()
• ✅ res.location()
• ✅ res.redirect()
• ✅ res.render()
• ✅ res.send()
• ✅ res.sendFile()
• • ✅ options.maxAge
• • ✅ options.root
• • ✅ options.lastModified
• • ✅ options.headers
• • ✅ options.dotfiles
• • ✅ options.acceptRanges
• • ✅ options.cacheControl
• • ✅ options.immutable
• • ✅ Range header
• • ✅ Setting ETag header
• • ✅ If-Match header
• • ✅ If-Modified-Since header
• • ✅ If-Unmodified-Since header
• • ✅ If-Range header
• ✅ res.sendStatus()
• ✅ res.header(), res.setHeader(), res.set()
• ✅ res.status()
• ✅ res.type()
• ✅ res.vary()
• ✅ res.removeHeader()
• ✅ res.write()
• ✅ res.writeHead()

Router

• ✅ router.all()
• ✅ router.METHOD() (router.get, router.post, etc.)
• ✅ router.route()
• ✅ router.use()
• ✅ router.param(name, callback)
• ✅ router.param(callback)
• ✅ options.caseSensitive
• ✅ options.strict
• ✅ options.mergeParams

Tested middlewares

Almost all middlewares that are compatible with Express are compatible with µExpress. Here's list of middlewares that we test for compatibility:

• ✅ body-parser (use express.text() etc instead for better performance)
• ✅ cookie-parser
• ✅ cookie-session
• ✅ compression
• ✅ serve-static (use express.static() instead for better performance)
• ✅ serve-index
• ✅ cors
• ✅ errorhandler
• ✅ method-override
• ✅ multer
• ✅ response-time
• ✅ express-fileupload
• ✅ express-session
• ✅ express-rate-limit
• ✅ express-subdomain
• ✅ vhost
• ✅ tsoa
• ✅ express-mongo-sanitize
• ✅ helmet
• ✅ passport
• ✅ morgan
• ✅ swagger-ui-express
• ✅ graphql-http
• ✅ better-sse

Middlewares and modules that are confirmed to not work:

• ❌ express-async-errors - doesn't work, use app.set('catch async errors', true) instead.

Tested view engines

Any Express view engine should work. Here's list of engines we include in our test suite:

• ✅ ejs
• ✅ pug
• ✅ express-dot-engine
• ✅ express-art-template
• ✅ express-handlebars
• ✅ swig