koa-router

What is koa-router?

koa-router is a powerful routing middleware for Koa, a next-generation web framework for Node.js. It allows you to define routes for your web application, handle HTTP methods, and manage middleware in a clean and organized manner.

What are koa-router's main functionalities?

Basic Routing

This code demonstrates how to set up a basic route using koa-router. When a GET request is made to the root URL '/', it responds with 'Hello World!'.

const Koa = require('koa');
const Router = require('koa-router');

const app = new Koa();
const router = new Router();

router.get('/', (ctx, next) => {
  ctx.body = 'Hello World!';
});

app.use(router.routes());
app.use(router.allowedMethods());

app.listen(3000);

Route Parameters

This code demonstrates how to use route parameters with koa-router. When a GET request is made to '/users/:id', it responds with the user ID provided in the URL.

const Koa = require('koa');
const Router = require('koa-router');

const app = new Koa();
const router = new Router();

router.get('/users/:id', (ctx, next) => {
  const userId = ctx.params.id;
  ctx.body = `User ID: ${userId}`;
});

app.use(router.routes());
app.use(router.allowedMethods());

app.listen(3000);

Middleware

This code demonstrates how to use middleware with koa-router. The logger middleware logs the HTTP method and URL of each request before passing control to the next middleware or route handler.

const Koa = require('koa');
const Router = require('koa-router');

const app = new Koa();
const router = new Router();

const logger = async (ctx, next) => {
  console.log(`${ctx.method} ${ctx.url}`);
  await next();
};

router.get('/', logger, (ctx, next) => {
  ctx.body = 'Hello World!';
});

app.use(router.routes());
app.use(router.allowedMethods());

app.listen(3000);

Nested Routes

This code demonstrates how to create nested routes with koa-router. The nestedRouter handles requests to '/nested/info' and responds with 'Nested Route Info'.

const Koa = require('koa');
const Router = require('koa-router');

const app = new Koa();
const router = new Router();
const nestedRouter = new Router();

nestedRouter.get('/info', (ctx, next) => {
  ctx.body = 'Nested Route Info';
});

router.use('/nested', nestedRouter.routes(), nestedRouter.allowedMethods());

app.use(router.routes());
app.use(router.allowedMethods());

app.listen(3000);

Other packages similar to koa-router

express

Express is a fast, unopinionated, minimalist web framework for Node.js. It provides robust routing capabilities similar to koa-router but is more widely used and has a larger ecosystem of middleware and plugins.

hapi

Hapi is a rich framework for building applications and services. It provides powerful configuration-based routing and extensive support for building scalable and maintainable applications. Compared to koa-router, Hapi offers more built-in features and a more opinionated structure.

restify

Restify is a framework specifically designed for building RESTful web services. It provides a similar routing mechanism to koa-router but is optimized for building APIs with a focus on performance and scalability.

README

koa-router

Router middleware for koa

• Express-style routing using app.get, app.put, app.post, etc.
• Named URL parameters.
• Named routes with URL generation.
• Responds to OPTIONS requests with allowed methods.
• Support for 405 Method Not Allowed and 501 Not Implemented.
• Multiple route middleware.
• Multiple routers.
• Nestable routers.
• ES7 async/await support.

Migrating to 7 / Koa 2

• The API has changed to match the new promise-based middleware signature of koa 2. See the koa 2.x readme for more information.
• Middleware is now always run in the order declared by .use() (or .get(), etc.), which matches Express 4 API.

Installation

Install using npm:

npm install koa-router

API Reference

• koa-router
  • Router ⏏
    • new Router([opts])
    • instance
      • .get|put|post|patch|delete|del ⇒ Router
      • .routes ⇒ function
      • .use([path], middleware) ⇒ Router
      • .prefix(prefix) ⇒ Router
      • .allowedMethods([options]) ⇒ function
      • .redirect(source, destination, [code]) ⇒ Router
      • .route(name) ⇒ Layer | false
      • .url(name, params, [options]) ⇒ String | Error
      • .param(param, middleware) ⇒ Router
    • static
      • .url(path, params) ⇒ String

Router ⏏

Kind: Exported class

new Router([opts])

Create a new router.

Param	Type	Description
[opts]	Object
[opts.prefix]	String	prefix router paths

Example
Basic usage:

var Koa = require('koa');
var Router = require('koa-router');

var app = new Koa();
var router = new Router();

router.get('/', (ctx, next) => {
  // ctx.router available
});

app
  .use(router.routes())
  .use(router.allowedMethods());

router.get|put|post|patch|delete|del ⇒ Router

Create router.verb() methods, where verb is one of the HTTP verbs such as router.get() or router.post().

Match URL patterns to callback functions or controller actions using router.verb(), where verb is one of the HTTP verbs such as router.get() or router.post().

Additionaly, router.all() can be used to match against all methods.

router
  .get('/', (ctx, next) => {
    ctx.body = 'Hello World!';
  })
  .post('/users', (ctx, next) => {
    // ...
  })
  .put('/users/:id', (ctx, next) => {
    // ...
  })
  .del('/users/:id', (ctx, next) => {
    // ...
  })
  .all('/users/:id', (ctx, next) => {
    // ...
  });

When a route is matched, its path is available at ctx._matchedRoute and if named, the name is available at ctx._matchedRouteName

Route paths will be translated to regular expressions using path-to-regexp.

Query strings will not be considered when matching requests.

Named routes

Routes can optionally have names. This allows generation of URLs and easy renaming of URLs during development.

router.get('user', '/users/:id', (ctx, next) => {
 // ...
});

router.url('user', 3);
// => "/users/3"

Multiple middleware

Multiple middleware may be given:

router.get(
  '/users/:id',
  (ctx, next) => {
    return User.findOne(ctx.params.id).then(function(user) {
      ctx.user = user;
      next();
    });
  },
  ctx => {
    console.log(ctx.user);
    // => { id: 17, name: "Alex" }
  }
);

Nested routers

Nesting routers is supported:

var forums = new Router();
var posts = new Router();

posts.get('/', (ctx, next) => {...});
posts.get('/:pid', (ctx, next) => {...});
forums.use('/forums/:fid/posts', posts.routes(), posts.allowedMethods());

// responds to "/forums/123/posts" and "/forums/123/posts/123"
app.use(forums.routes());

Router prefixes

Route paths can be prefixed at the router level:

var router = new Router({
  prefix: '/users'
});

router.get('/', ...); // responds to "/users"
router.get('/:id', ...); // responds to "/users/:id"

URL parameters

Named route parameters are captured and added to ctx.params.

router.get('/:category/:title', (ctx, next) => {
  console.log(ctx.params);
  // => { category: 'programming', title: 'how-to-node' }
});

The path-to-regexp module is used to convert paths to regular expressions.

Kind: instance property of Router

Param	Type	Description
path	String
[middleware]	function	route middleware(s)
callback	function	route callback

router.routes ⇒ function

Returns router middleware which dispatches a route matching the request.

Kind: instance property of Router

router.use([path], middleware) ⇒ Router

Use given middleware.

Middleware run in the order they are defined by .use(). They are invoked sequentially, requests start at the first middleware and work their way "down" the middleware stack.

Kind: instance method of Router

Param	Type
[path]	String
middleware	function
[...]	function

Example

// session middleware will run before authorize
router
  .use(session())
  .use(authorize());

// use middleware only with given path
router.use('/users', userAuth());

// or with an array of paths
router.use(['/users', '/admin'], userAuth());

app.use(router.routes());

router.prefix(prefix) ⇒ Router

Set the path prefix for a Router instance that was already initialized.

Kind: instance method of Router

Param	Type
prefix	String

Example

router.prefix('/things/:thing_id')

router.allowedMethods([options]) ⇒ function

Returns separate middleware for responding to OPTIONS requests with an Allow header containing the allowed methods, as well as responding with 405 Method Not Allowed and 501 Not Implemented as appropriate.

Kind: instance method of Router

Param	Type	Description
[options]	Object
[options.throw]	Boolean	throw error instead of setting status and header
[options.notImplemented]	function	throw the returned value in place of the default NotImplemented error
[options.methodNotAllowed]	function	throw the returned value in place of the default MethodNotAllowed error

Example

var Koa = require('koa');
var Router = require('koa-router');

var app = new Koa();
var router = new Router();

app.use(router.routes());
app.use(router.allowedMethods());

Example with Boom

var Koa = require('koa');
var Router = require('koa-router');
var Boom = require('boom');

var app = new Koa();
var router = new Router();

app.use(router.routes());
app.use(router.allowedMethods({
  throw: true,
  notImplemented: () => new Boom.notImplemented(),
  methodNotAllowed: () => new Boom.methodNotAllowed()
}));

router.redirect(source, destination, [code]) ⇒ Router

Redirect source to destination URL with optional 30x status code.

Both source and destination can be route names.

router.redirect('/login', 'sign-in');

This is equivalent to:

router.all('/login', ctx => {
  ctx.redirect('/sign-in');
  ctx.status = 301;
});

Kind: instance method of Router

Param	Type	Description
source	String	URL or route name.
destination	String	URL or route name.
[code]	Number	HTTP status code (default: 301).

router.route(name) ⇒ Layer | false

Lookup route with given name.

Kind: instance method of Router

Param	Type
name	String

router.url(name, params, [options]) ⇒ String | Error

Generate URL for route. Takes a route name and map of named params.

Kind: instance method of Router

Param	Type	Description
name	String	route name
params	Object	url parameters
[options]	Object	options parameter
[options.query]	Object | String	query options

Example

router.get('user', '/users/:id', (ctx, next) => {
  // ...
});

router.url('user', 3);
// => "/users/3"

router.url('user', { id: 3 });
// => "/users/3"

router.use((ctx, next) => {
  // redirect to named route
  ctx.redirect(ctx.router.url('sign-in'));
})

router.url('user', { id: 3 }, { query: { limit: 1 } });
// => "/users/3?limit=1"

router.url('user', { id: 3 }, { query: "limit=1" });
// => "/users/3?limit=1"

router.param(param, middleware) ⇒ Router

Run middleware for named route parameters. Useful for auto-loading or validation.

Kind: instance method of Router

Param	Type
param	String
middleware	function

Example

router
  .param('user', (id, ctx, next) => {
    ctx.user = users[id];
    if (!ctx.user) return ctx.status = 404;
    return next();
  })
  .get('/users/:user', ctx => {
    ctx.body = ctx.user;
  })
  .get('/users/:user/friends', ctx => {
    return ctx.user.getFriends().then(function(friends) {
      ctx.body = friends;
    });
  })
  // /users/3 => {"id": 3, "name": "Alex"}
  // /users/3/friends => [{"id": 4, "name": "TJ"}]

Router.url(path, params) ⇒ String

Generate URL from url pattern and given params.

Kind: static method of Router

Param	Type	Description
path	String	url pattern
params	Object	url parameters

Example

var url = Router.url('/users/:id', {id: 1});
// => "/users/1"

Contributing

Please submit all issues and pull requests to the alexmingoia/koa-router repository!

Tests

Run tests using npm test.

Support

If you have any problem or suggestion please open an issue here.

Changelog

7.4.0

• Fix router.url() for multiple nested routers #407
• layer.name added to ctx at ctx.routerName during routing #412
• Router.use() was erroneously settings (.*) as a prefix to all routers nested with .use that did not pass an explicit prefix string as the first argument. This resulted in routes being matched that should not have been, included the running of multiple route handlers in error. #369 and #410 include information on this issue.