Routing

Web servers use the request's path and HTTP method to look up the correct resource, refers as "routing".

We can define a route by calling a method named after HTTP verbs, passing a path and a function to execute when matched.

import { Elysia } from 'elysia'

new Elysia()
    .get('/', 'hello')
    .get('/hi', 'hi')
    .listen(3000)

We can access the web server by going to http://localhost:3000

By default, web browsers will send a GET method when visiting a page.

localhost//hi

GET

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Using an interactive browser above, hover on a blue highlight area to see difference result between each path

Path type

Path in Elysia can be grouped into 3 types:

• static paths - static string to locate the resource
• dynamic paths - segment can be any value
• wildcards - path until a specific point can be anything

You can use all of the path types together to compose a behavior for your web server.

The priorities are as follows:

1. static paths
2. dynamic paths
3. wildcards

If the path is resolved as the static wild dynamic path is presented, Elysia will resolve the static path rather than the dynamic path

import { Elysia } from 'elysia'

new Elysia()
    .get('/id/1', 'static path')
    .get('/id/:id', 'dynamic path')
    .get('/id/*', 'wildcard path')
    .listen(3000)

localhost/id/1/id/2/id/2/a

GET

Here the server will respond as follows:

Path	Response
/id/1	static path
/id/2	dynamic path
/id/2/a	wildcard path

Static Path

A path or pathname is an identifier to locate resources of a server.

http://localhost:/path/page

Elysia uses the path and method to look up the correct resource.

A path starts after the origin. Prefix with / and ends before search query (?)

We can categorize the URL and path as follows:

URL	Path
http://site.com/	/
http://site.com/hello	/hello
http://site.com/hello/world	/hello/world
http://site.com/hello?name=salt	/hello
http://site.com/hello#title	/hello

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If the path is not specified, the browser and web server will treat the path as '/' as a default value.

Elysia will look up each request for route and response using handler function.

Dynamic path

URLs can be both static and dynamic.

Static paths are hardcoded strings that can be used to locate resources of the server, while dynamic paths match some part and captures the value to extract extra information.

For instance, we can extract the user ID from the pathname. For example:

import { Elysia } from 'elysia'

new Elysia()
    .get('/id/:id', ({ params: { id } }) => id)
    .listen(3000)

Here dynamic path is created with /id/:id which tells Elysia to match any path up until /id. What comes after that is then stored as params object.

localhost/id/1/id/123/id/anything/id/id/anything/test

GET

1

When requested, the server should return the response as follows:

Path	Response
/id/1	1
/id/123	123
/id/anything	anything
/id/anything?name=salt	anything
/id	Not Found
/id/anything/rest	Not Found

Dynamic paths are great to include things like IDs, which then can be used later.

We refer to the named variable path as path parameter or params for short.

Segment

URL segments are each path that is composed into a full path.

Segments are separated by /.

Path parameters in Elysia are represented by prefixing a segment with ':' followed by a name.

Path parameters allow Elysia to capture a specific segment of a URL.

The named path parameter will then be stored in Context.params.

Route	Path	Params
/id/:id	/id/1	id=1
/id/:id	/id/hi	id=hi
/id/:name	/id/hi	name=hi

Multiple path parameters

You can have as many path parameters as you like, which will then be stored into a params object.

import { Elysia } from 'elysia'

new Elysia()
    .get('/id/:id', ({ params: { id } }) => id)
    .get('/id/:id/:name', ({ params: { id, name } }) => id + ' ' + name)
    .listen(3000)

localhost/id/1/id/123/id/anything/id/id/anything/rest

GET

1

The server will respond as follows:

Path	Response
/id/1	1
/id/123	123
/id/anything	anything
/id/anything?name=salt	anything
/id	Not Found
/id/anything/rest	anything rest

Optional path parameters

Sometime we might want a static and dynamic path to resolve the same handler.

We can make a path parameter optional by adding a question mark ? after the parameter name.

import { Elysia } from 'elysia'

new Elysia()
    .get('/id/:id?', ({ params: { id } }) => `id ${id}`)
    .listen(3000)

localhost/get/post/m-search

GET

The server will respond as follows:

Path	Response
/id	id undefined
/id/1	id 1

Wildcards

Dynamic paths allow capturing certain segments of the URL.

However, when you need a value of the path to be more dynamic and want to capture the rest of the URL segment, a wildcard can be used.

Wildcards can capture the value after segment regardless of amount by using "*".

import { Elysia } from 'elysia'

new Elysia()
    .get('/id/*', ({ params }) => params['*'])
    .listen(3000)

localhost/id/1/id/123/id/anything/id/id/anything/rest

GET

1

In this case the server will respond as follows:

Path	Response
/id/1	1
/id/123	123
/id/anything	anything
/id/anything?name=salt	anything
/id	Not Found
/id/anything/rest	anything/rest

Wildcards are useful for capturing a path until a specific point.

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You can use a wildcard with a path parameter.

HTTP Verb

HTTP defines a set of request methods to indicate the desired action to be performed for a given resource

There are several HTTP verbs, but the most common ones are:

GET

Requests using GET should only retrieve data.

POST

Submits a payload to the specified resource, often causing state change or side effect.

PUT

Replaces all current representations of the target resource using the request's payload.

Patch

Applies partial modifications to a resource.

DELETE

Deletes the specified resource.

---

To handle each of the different verbs, Elysia has a built-in API for several HTTP verbs by default, similar to Elysia.get

import { Elysia } from 'elysia'

new Elysia()
    .get('/', 'hello')
    .post('/hi', 'hi')
    .listen(3000)

localhost//hi

GET

Elysia HTTP methods accepts the following parameters:

• path: Pathname
• function: Function to respond to the client
• hook: Additional metadata

You can read more about the HTTP methods on HTTP Request Methods.

Custom Method

We can accept custom HTTP Methods with Elysia.route.

import { Elysia } from 'elysia'

const app = new Elysia()
    .get('/get', 'hello')
    .post('/post', 'hi')
    .route('M-SEARCH', '/m-search', 'connect') 
    .listen(3000)

localhost/id/id/:id

GET

Elysia.route accepts the following:

• method: HTTP Verb
• path: Pathname
• function: Function to response to the client
• hook: Additional metadata

When navigating to each method, you should see the results as the following:

Path	Method	Result
/	GET	hello
/	POST	hi
/	M-SEARCH	connect

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Based on RFC 7231, HTTP Verb is case-sensitive.

It's recommended to use the UPPERCASE convention for defining a custom HTTP Verb with Elysia.

Elysia.all

Elysia provides an Elysia.all for handling any HTTP method for a specified path using the same API like Elysia.get and Elysia.post

import { Elysia } from 'elysia'

new Elysia()
    .all('/', 'hi')
    .listen(3000)

localhost//

GET

Any HTTP method that matches the path, will be handled as follows:

Path	Method	Result
/	GET	hi
/	POST	hi
/	DELETE	hi

Handle

Most developers use REST clients like Postman, Insomnia or Hoppscotch to test their API.

However, Elysia can be programmatically test using Elysia.handle.

import { Elysia } from 'elysia'

const app = new Elysia()
    .get('/', 'hello')
    .post('/hi', 'hi')
    .listen(3000)

app.handle(new Request('http://localhost/')).then(console.log)

Elysia.handle is a function to process an actual request sent to the server.

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Unlike unit test's mock, you can expect it to behave like an actual request sent to the server.

But also useful for simulating or creating unit tests.

404

If no path matches the defined routes, Elysia will pass the request to error life cycle before returning a "NOT_FOUND" with an HTTP status of 404.

We can handle a custom 404 error by returning a value from 'error` life cycle like this:

import { Elysia } from 'elysia'

new Elysia()
    .get('/', 'hi')
    .onError(({ code }) => {
        if (code === 'NOT_FOUND') {
            return 'Route not found :('
        }
    })
    .listen(3000)

localhost//hi

GET

When navigating to your web server, you should see the result as follows:

Path	Method	Result
/	GET	hi
/	POST	Route not found :(
/hi	GET	Route not found :(

You can learn more about life cycle and error handling in Life Cycle Events and Error Handling.

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HTTP Status is used to indicate the type of response. By default if everything is correct, the server will return a '200 OK' status code (If a route matches and there is no error, Elysia will return 200 as default)

If the server fails to find any route to handle, like in this case, then the server shall return a '404 NOT FOUND' status code.

Group

When creating a web server, you would often have multiple routes sharing the same prefix:

import { Elysia } from 'elysia'

new Elysia()
    .post('/user/sign-in', 'Sign in')
    .post('/user/sign-up', 'Sign up')
    .post('/user/profile', 'Profile')
    .listen(3000)

localhost/user/sign-in/user/sign-up/user/profile

POST

This can be improved with Elysia.group, allowing us to apply prefixes to multiple routes at the same time by grouping them together:

import { Elysia } from 'elysia'

new Elysia()
    .group('/user', (app) =>
        app
            .post('/sign-in', 'Sign in')
            .post('/sign-up', 'Sign up')
            .post('/profile', 'Profile')
    )
    .listen(3000)

localhost/user/sign-in/user/sign-up/user/profile

POST

This code behaves the same as our first example and should be structured as follows:

Path	Result
/user/sign-in	Sign in
/user/sign-up	Sign up
/user/profile	Profile

.group() can also accept an optional guard parameter to reduce boilerplate of using groups and guards together:

import { Elysia, t } from 'elysia'

new Elysia()
    .group(
        '/user',
        {
            body: t.Literal('Rikuhachima Aru')
        },
        (app) => app
            .post('/sign-in', 'Sign in')
            .post('/sign-up', 'Sign up')
            .post('/profile', 'Profile')
    )
    .listen(3000)

You may find more information about grouped guards in scope.

Prefix

We can separate a group into a separate plugin instance to reduce nesting by providing a prefix to the constructor.

import { Elysia } from 'elysia'

const users = new Elysia({ prefix: '/user' })
    .post('/sign-in', 'Sign in')
    .post('/sign-up', 'Sign up')
    .post('/profile', 'Profile')

new Elysia()
    .use(users)
    .get('/', 'hello world')
    .listen(3000)

localhost//user/sign-in/user/sign-up/user/profile

GET