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    0.3.3 • Public • Published


    A micro web server so fast, it'll make you dance! 👯

    Polka is an extremely minimal, highly performant Express.js alternative. Yes, you're right, Express is already super fast & not that big 🤔 — but Polka shows that there was (somehow) room for improvement!

    Essentially, Polka is just a native HTTP server with added support for routing, middleware, and sub-applications. That's it! 🎉

    And, of course, in mandatory bullet-point format:

    • 33-50% faster than Express for simple applications
    • Middleware support, including Express middleware you already know & love
    • Nearly identical application API & route pattern definitions
    • ~90 LOC for Polka, 120 including its router


    $ npm install --save polka


    const polka = require('polka');
    function one(req, res, next) {
      req.hello = 'world';
    function two(req, res, next) { = '...needs better demo 😔';
      .use(one, two)
      .get('/users/:id', (req, res) => {
        console.log(`~> Hello, ${req.hello}`);
        res.end(`User: ${}`);
      .listen(3000).then(_ => {
        console.log(`> Running on localhost:3000`);


    Polka extends Trouter which means it inherits its API, too!


    Returns an instance of Polka~!


    Type: Function

    A catch-all error handler; executed whenever a middleware throws an error. Change this if you don't like default behavior.

    Its signature is (err, req, res, next), where err is the String or Error thrown by your middleware.

    Caution: Use next() to bypass certain errors at your own risk!
    You must be certain that the exception will be handled elsewhere or can be safely ignored.
    Otherwise your response will never terminate!


    Type: Function

    A handler when no route definitions were matched. Change this if you don't like default behavior, which sends a 404 status & Not found response.

    Its signature is (req, res) and requires that you terminate the response.

    use(base, ...fn)

    Attach middleware(s) and/or sub-application(s) to the server. These will execute before your routes' handlers.

    Important: If a base pathname is provided, all functions within the same use() block will only execute when the req.pathname matches the base path.


    Type: String
    Default: undefined

    The base path on which the following middleware(s) or sub-application should be mounted.


    Type: Function|Array

    You may pass one or more functions at a time. Each function must have the standardized (req, res, next) signature.

    You may also pass a sub-application, which must be accompanied by a base pathname.

    Please see Middleware and Express' middleware examples for more info.


    Returns: Object

    This is an alias of the awesome parseurl module. There are no Polka-specific changes.

    listen(port, hostname)

    Returns: Promise

    Wraps the native server.listen with a Promise, rejecting on any error.

    handler(req, res, parsed)

    The main Polka ClientRequest handler. It receives all requests and tries to match the incoming URL against known routes.

    If the req.url is not immediately matched, Polka will look for sub-applications or middleware groups matching the req.url's base path. If any are found, they are appended to the loop, running after any global middleware.

    Note: Any middleware defined within a sub-application is run after the main app's (aka, global) middleware and before the sub-application's route handler.

    At the end of the loop, if a middleware hasn't yet terminated the response (or thrown an error), the route handler will be executed, if found — otherwise a (404) Not found response is returned, configurable via options.onNoMatch.


    Type: ClientRequest


    Type: ServerResponse


    Type: Object

    Optionally provide a parsed URL object. Useful if you've already parsed the incoming path. Otherwise, app.parse (aka parseurl) will run by default.


    Routes are used to define how an application responds to varying HTTP methods and endpoints.

    If you're coming from Express, there's nothing new here!
    However, do check out Comparisons for some pattern changes.


    Each route is comprised of a path pattern, a HTTP method, and a handler (aka, what you want to do).

    In code, this looks like:

    app.METHOD(pattern, handler);


    • app is an instance of polka
    • METHOD is any valid HTTP method, lowercased
    • pattern is a routing pattern (string)
    • handler is the function to execute when pattern is matched

    Also, a single pathname (or pattern) may be reused with multiple METHODs.

    The following example demonstrates some simple routes.

    const app = polka();
    app.get('/', (req, res) => {
      res.end('Hello world!');
    app.get('/users', (req, res) => {
      res.end('Get all users!');
    });'/users', (req, res) => {
      res.end('Create a new User!');
    app.put('/users/:id', (req, res) => {
      res.end(`Update User with ID of ${}`);
    app.delete('/users/:id', (req, res) => {
      res.end(`CY@ User ${}!`);


    Unlike the very popular path-to-regexp, Polka uses string comparison to locate route matches. While faster & more memory efficient, this does also prevent complex pattern matching.

    However, have no fear! 💥 All the basic and most commonly used patterns are supported. You probably only ever used these patterns in the first place. 😉

    See Comparisons for the list of RegExp-based patterns that Polka does not support.

    The supported pattern types are:

    • static (/users)
    • named parameters (/users/:id)
    • nested parameters (/users/:id/books/:title)
    • optional parameters (/users/:id?/books/:title?)
    • any match / wildcards (/users/*)


    Any named parameters included within your route pattern will be automatically added to your incoming req object. All parameters will be found within req.params under the same name they were given.

    Important: Your parameter names should be unique, as shared names will overwrite each other!

    app.get('/users/:id/books/:title', (req, res) => {
      let { id, title } = req.params;
      res.end(`User: ${id} && Book: ${title}`);
    $ curl /users/123/books/Narnia
    #=> User: 123 && Book: Narnia


    Any valid HTTP method is supported! However, only the most common methods are used throughout this documentation for demo purposes.

    Note: For a full list of valid METHODs, please see this list.


    Request handlers accept the incoming ClientRequest and the formulating ServerResponse.

    Every route definition must contain a valid handler function, or else an error will be thrown at runtime.

    Important: You must always terminate a ServerResponse!

    It's a very good practice to always terminate your response (res.end) inside a handler, even if you expect a middleware to do it for you. In the event a response is/was not terminated, the server will hang & eventually exit with a TIMEOUT error.

    Note: This is a native http behavior.

    Async Handlers

    If using Node 7.4 or later, you may leverage native async and await syntax! 😻

    No special preparation is needed — simply add the appropriate keywords.

    const app = polka();
    const sleep = ms => new Promise(r => setTimeout(r, ms));
    async function authenticate(req, res, next) {
      let token = req.getHeader('authorization');
      if (!token) return app.send(res, 401);
      req.user = await Users.find(token); // <== fake
      next(); // done, woot!
      .get('/', async (req, res) => {
        // log middleware's findings
        console.log('~> current user', req.user);
        // force sleep, because we can~!
        await sleep(500);
        // send greeting
        res.end(`Hello, ${}`);


    Middleware are functions that run in between (hence "middle") receiving the request & executing your route's handler response.

    Coming from Express? Use any middleware you already know & love! 🎉

    The middleware signature receives the request (req), the response (res), and a callback (next).

    These can apply mutations to the req and res objects, and unlike Express, have access to req.params, req.pathname,, and req.query!

    Most importantly, a middleware must either call next() or terminate the response (res.end). Failure to do this will result in a never-ending response, which will eventually crash the http.Server.

    // Log every request
    function logger(req, res, next) {
      console.log(`~> Received ${req.method} on ${req.url}`);
      next(); // move on
    function authorize(req, res, next) {
      // mutate req; available later
      req.token = req.getHeader('authorization');
      req.token ? next() : ((res.statusCode=401) && res.end('No token!'));
    polka().use(logger, authorize).get('*', (req, res) => {
      console.log(`~> user token: ${req.token}`);
      res.end('Hello, valid user');
    $ curl /
    # ~> Received GET on /
    #=> (401) No token!
    $ curl -H "authorization: secret" /foobar
    # ~> Received GET on /foobar
    # ~> user token: secret
    #=> (200) Hello, valid user

    In Polka, middleware functions are mounted globally, which means that they'll run on every request (see Comparisons). Instead, you'll have to apply internal filters to determine when & where your middleware should run.

    Note: This might change in Polka 1.0 🤔

    function foobar(req, res, next) {
      if (req.pathname.startsWith('/users')) {
        // do something magical

    Middleware Errors

    If an error arises within a middleware, the loop will be exited. This means that no other middleware will execute & neither will the route handler.

    Similarly, regardless of statusCode, an early response termination will also exit the loop & prevent the route handler from running.

    There are three ways to "throw" an error from within a middleware function.

    Hint: None of them use throw 😹

    1. Pass any string to next()

      This will exit the loop & send a 500 status code, with your error string as the response body.

        .use((req, res, next) => next('💩'))
        .get('*', (req, res) => res.end('wont run'));
      $ curl /
      #=> (500) 💩
    2. Pass an Error to next()

      This is similar to the above option, but gives you a window in changing the statusCode to something other than the 500 default.

      function oopsies(req, res, next) {
        let err = new Error('Try again');
        err.code = 422;
      $ curl /
      #=> (422) Try again
    3. Terminate the response early

      Once the response has been ended, there's no reason to continue the loop!

      This approach is the most versatile as it allows to control every aspect of the outgoing res.

      function oopsies(req, res, next) {
        if (true) {
          // something bad happened~
          res.writeHead(400, {
            'Content-Type': 'application/json',
            'X-Error-Code': 'Please dont do this IRL'
          let json = JSON.stringify({ error:'Missing CSRF token' });
        } else {
          next(); // never called FYI
      $ curl /
      #=> (400) {"error":"Missing CSRF token"}


    A round of Polka-vs-Express benchmarks across varying Node versions can be found here.

    Important: Time is mostly spent in your application code rather than Express or Polka code!
    Switching from Express to Polka will (likely) not show such drastic performance gains.

    Node 8.9.0
        Thread Stats   Avg      Stdev     Max   +/- Stdev
            Latency     2.24ms  124.41us   6.77ms   88.78%
            Req/Sec     5.38k   144.35     6.26k    94.30%
          432249 requests in 10.10s, 42.87MB read
        Requests/sec:  42784.60
        Transfer/sec:      4.24MB
        Thread Stats   Avg      Stdev     Max   +/- Stdev
            Latency     2.26ms  138.41us   6.66ms   90.94%
            Req/Sec     5.33k    83.07     5.94k    80.25%
          424080 requests in 10.01s, 42.06MB read
        Requests/sec:  42381.02
        Transfer/sec:      4.20MB
        Thread Stats   Avg      Stdev     Max   +/- Stdev
            Latency     5.15ms  421.69us   8.51ms   77.95%
            Req/Sec     2.34k    77.06     2.55k    72.12%
          186390 requests in 10.01s, 36.97MB read
        Requests/sec:  18628.36
        Transfer/sec:      3.70MB
        Thread Stats   Avg      Stdev     Max   +/- Stdev
            Latency     2.91ms  201.13us   7.51ms   58.07%
            Req/Sec     4.14k   130.04     4.48k    65.59%
          333158 requests in 10.10s, 41.30MB read
        Requests/sec:  32979.84
        Transfer/sec:      4.09MB
        Thread Stats   Avg      Stdev     Max   +/- Stdev
            Latency     3.43ms  369.96us   8.67ms   87.30%
            Req/Sec     3.51k   114.78     4.12k    69.76%
          281808 requests in 10.10s, 38.97MB read
        Requests/sec:  27892.99
        Transfer/sec:      3.86MB


    Polka's API aims to be very similar to Express since most Node.js developers are already familiar with it. If you know Express, you already know Polka! 💃

    There are, however, a few main differences. Polka does not support or offer:

    1. Any built-in view/rendering engines.

      Most templating engines can be incorporated into middleware functions or used directly within a route handler.

    2. The ability to throw from within middleware.

      However, all other forms of middleware-errors are supported. (See Middleware Errors.)

      function middleware(res, res, next) {
        // pass an error message to next()
        next('uh oh');
        // pass an Error to next()
        next(new Error('🙀'));
        // send an early, customized error response
        res.statusCode = 401;
        res.end('Who are you?');
    3. Express-like response helpers... yet! (#14)

      Express has a nice set of response helpers. While Polka relies on the native Node.js response methods, it would be very easy/possible to attach a global middleware that contained a similar set of helpers. (TODO)

    4. RegExp-based route patterns.

      Polka's router uses string comparison to match paths against patterns. It's a lot quicker & more efficient.

      The following routing patterns are not supported:

      app.get('/ab?cd', _ => {});
      app.get('/ab+cd', _ => {});
      app.get('/ab*cd', _ => {});
      app.get('/ab(cd)?e', _ => {});
      app.get(/a/, _ => {});
      app.get(/.*fly$/, _ => {});

      The following routing patterns are supported:

      app.get('/users', _ => {});
      app.get('/users/:id', _ => {});
      app.get('/users/:id?', _ => {});
      app.get('/users/:id/books/:title', _ => {});
      app.get('/users/*', _ => {});


    MIT © Luke Edwards




    npm i polka@0.3.3





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