Routing is the process of determining what code to run when a URL is requested.

router is a JS router, which works client-side (browser), or server-side (NodeJS).

router resolves URL paths like /profile/1 to route patterns such as /profile/:id, and generates a params object that is passed to each route.

router also provides some basic web server features if routing HTTP requests - parses req.body into params, uses expressjs-like API, supports middleware.

Features

• Easy setup, zero dependencies
• Only 2kb minified and gzipped
• Simple syntax and usage
• Works client-side, in browsers:
  • as a router for single page applications (SPAs)
• Works server-side, in Node:
  • as a router for an HTTP server (express.js like API, also supports "middleware")
  • as a router in an AWS Lambda (routing of the event data passed into Lambda)
• Works in the terminal as an args parser for command-line programs

Basic syntax example

IMPORTANT! You must use the name router, and not something else.

  router({

    '/home':                  (params) => { ... },

    '/profile/:id':           (params) => { ... },

    '/profile/:id/user/:uId': (params) => { ... },

  });

The supported route pattern types are:

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

Installation

In browsers:

<script src="https://unpkg.com/@scottjarvis/router"></script>
<script>
  // use router here
</script>

In NodeJS:

npm i @scottjarvis/router

Then add it to your project:

router = require('@scottjarvis/router');

// use router here

Usage in browsers: as a client-side router

For routing frontend JS stuff like "single page applications", you'll need to trigger the router when the URL changes, or a link is clicked.

router is designed to be used with window.location.hash and hashchange.

Here' an example of how to bind the router to URL changes in the browser:

  // 1. capture link clicks for links such as  <a href="#/profile/1">some text</a>

  window.addEventListener(
    "click",
    function handleLink(e) {
      if (!e.target.matches("a")) return
      if (!e.target.href.matches(/^#/)) return
      e.preventDefault()
      location.hash = e.target.hash
    },
    false
  )

  // 2. monitor changes to window.location.hash, and run the router when it changes

  window.addEventListener(
    "hashchange",
    function(e) {
      router.href(window.location.hash)
    },
    false
  )

See the full example in examples/client-side-router.html

Usage in NodeJS: as a HTTP web server

You could simply use router inside a standard NodeJS http server, with it's provided methods res.writeHead(), res.write() and res.end() (see this nice guide to the NodeJS http module).

However, router provides some simple wrappers around these methods, just like express.js.

Here's an example of routing HTTP requests in your NodeJS based web server:

var http = require("http")
var router = require("router")

http.createServer((req, res) => {

  router(
    {
      "/home": params => {
        console.log("home!", params)
        // set header status to "200",
        // set content-type to "text/html",
        // set content, end response
        res.send("<p>some string</p>")
      },
      "/user/:userId": params => {
        console.log("serving JSON!", params)
        // set header to "200" manually
        // set content-type to "application/json",
        // set content (prettified JSON)
        // end response
        res.status(200)
        res.send(params)
      },
      // any other route
      "*": params => {
        res.send("<h1>API Docs:</h1>")
      }
    },
    // for servers, you must pass in 'req' and 'res', after the routes object above
    req, res
  )

})

There is a res.status() method, which sets res.statusCode for you.

There is a res.send() method, which makes life easier for you:

• sets appropriate header status to 200 (if res.status() not used)
• sets appropriate content type:
  • text/html - if given a string
  • application/json - if given an object, array or JSON
  • application/octet-stream - if given a Buffer
• pretty prints JSON output
• calls res.end() for you

The res.json() method is similar to above, but sends the Content-Type application/json.

The res.jsonp() is similar to res.json(), but sends the Content-Type text/javascript and wraps your JSON in a callback, like so:

callback({ some: \"data\" })

Using HTTP "middleware"

If running an HTTP server (or Lambda, see below), router supports "middleware", in a similar way to express.js.

Some express middleware may work with router, though this has not been tested.

Creating middleware for router is very simple - define a function that takes (req, res, next) as parameters:

var getRequestTime = function(req, res, next) {
  req.time = Date.now()
  console.log("middleware: added req.time: ", req.time)
  next()
}

And do router.use(someFunc) to enable it:

// pass the middleware function to router.use()
router.use(getRequestTime)

Or enable middleware for specific routes:

router.use("/home", getRequestTime)

You can also pass an array of middlewares:

router.use([func1, func2, func3])

Or any array of middlewares to run on a specific route:

router.use('/home', [func1, func2, func3])

See the full example in examples/http-router.js

About HTTP request body parsing:

In NodeJS HTTP servers, the HTTP request "body" is received in "chunks" - you must normally combine & parse these chunks in order to get access to the whole req.body data.

So to make life easier, router does this basic parsing of the HTTP request body for you, so that it's readily available in the params passed to your routes:

1. The req.body chunks received are combined into a string, available as req.body in your routes.
2. If req.body is a URL-encoded or JSON-encoded string, router will convert it to a JS object, and also add its properties to params. For example, the original req.body may be ?user=bob&id=1 - this will be parsed for you and available as params.user and params.id.

Therefore, when inside your routes, there's often no need to parse req.body yourself - unless handling gzipped data or file uploads (multi-part form data or octect-streams). In this case, you should use middleware like body-parser.

If you're running a GET-based restful API, you probably don't need to worry about req.body, it's usually only for POST data and file uploads.

Usage in AWS Lambda: as router for your API

Here's an example of using router in an AWS Lambda:

'use strict';
var router = require("@scottjarvis/router")

exports.handler = (event, context, callback) => {
  router(
    {
      "/ping": params => {
        // do stuff here
        callback(null, params)
      },

      "/user/:userId": params => {
        // do stuff here
        var resp = { ... }
        callback(null, resp)
      }
    },
    // for Lambdas, you must pass in 'event', 'context' and 'callback'
    event,
    context,
    callback
  )
}

In Lambdas, router works out which route to run from the event.path property (not from any HTTP req objects).

To make life easier inside your routes:

1. If event.body is URL-encoded or JSON-encoded, it'll be parsed into a JavaScript object.
2. If event.body was parsed into a JavaScript object, its properties will be added into params.
3. The params object should have everything needed for a valid response object, so it can be passed straight to callback() (or returned, if running in an async Lambda).

Using Lambda "middleware"

There is currently very basic middleware support for Lambdas:

• Lambda middleware functions take (event, next) as parameters
• so you should read or modify event, instead of req and res
• it should otherwise be similar to using HTTP middleware :)

Here's how to define some Lambda middleware:

var getRequestTime = function(event, next) {
  event.time = Date.now()
  console.log("middleware: added event.time: ", event.time)
  next()
}

And just pass the middleware function to router.use():

router.use(getRequestTime)

If you need a more advanced Lambda router, see middy.

See the full example in examples/lambda-router.js.

Usage in NodeJS: as a CLI args parser

If you building a NodeJS program, you might want an easy way to parse the command line arguments it receives.

If so, router can help - it auto maps command-line arguments to the params object received by your routes:

node some_script.js --foo=bar --verbose --dir=/home

will be matched in some_script.js by using something like:

var router = require("../src/router.js")

router({

  // 'params' will contain all command-line arguments
  // that were passed to this script

  "*": params => {
    console.log(params) // { foo: "bar", verbose: true, dir: "/home" }
  }

})

See the full example in examples/cli-router.js.

Making changes to router

Look in src/router.js, make any changes you like.

Rebuild the bundles in dist/ using this command: npm run build

Related projects:

Alternative routers

• director - a fairly small, isomorphic URL router for JavaScript
• hasher - Tiny hashchange router inspired by express.js & page.js
• routie - a tiny javascript hash router
• trouter - a fast, small-but-mighty, familiar router
• RouterRouter - a tiny JS router, extracted from Backbone's Router
• gcpantazis/router.js - a very simple router based on BackboneJS Router

Alternative HTTP servers

• expressJS - the most widely used JavaScript server, with routing "middleware"
• polka - minimal, performant expressjs alternative (uses trouter)
• middy - a popular router for AWS Lambda, uses a middleware-style API

Acknowledgements

• Zetcode: javascript/http
• @pyaesonekhant1234: differences-between-res-write-res-end-and-res-send
• Okta.com: Build and understand express middleware through examples
• Towards Data Science: Building your own router for AWS Lambda
• vkhazin/aws-lambda-http-router

Further improvements

"express-compat" middleware

A middleware that adds the same properties and methods to req and res as express.js.

This should improve compatibility with other express.js middleware that is loaded after.

Basic auth middleware

See

• https://github.com/jshttp/basic-auth
• https://github.com/arkerone/api-key-auth

JSWT auth middleware

See https://github.com/auth0/node-jsonwebtoken

Error handling middleware

See https://github.com/expressjs/api-error-handler