Cheat Sheet

Here are a quick overview for a common Elysia patterns

Hello World

A simple hello world

import { Elysia } from 'elysia'

new Elysia()
    .get('/', () => 'Hello World')
    .listen(3000)

Custom HTTP Method

Define route using custom HTTP methods/verbs

See Route

import { Elysia } from 'elysia'

new Elysia()
    .get('/hi', () => 'Hi')
    .post('/hi', () => 'From Post')
    .put('/hi', () => 'From Put')
    .route('M-SEARCH', '/hi', () => 'Custom Method')
    .listen(3000)

Path Parameter

Using dynamic path parameter

See Path

import { Elysia } from 'elysia'

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

Return JSON

Elysia converts response to JSON automatically

See Handler

import { Elysia } from 'elysia'

new Elysia()
    .get('/json', () => {
        return {
            hello: 'Elysia'
        }
    })
    .listen(3000)

Return a file

A file can be return in as formdata response

The response must be a 1-level deep object

import { Elysia, file } from 'elysia'

new Elysia()
    .get('/json', () => {
        return {
            hello: 'Elysia',
            image: file('public/cat.jpg')
        }
    })
    .listen(3000)

Header and status

Set a custom header and a status code

See Handler

import { Elysia } from 'elysia'

new Elysia()
    .get('/', ({ set, error }) => {
        set.headers['x-powered-by'] = 'Elysia'

        return error(418, "I'm a teapot")
    })
    .listen(3000)

Group

Define a prefix once for sub routes

See Group

import { Elysia } from 'elysia'

new Elysia()
    .get("/", () => "Hi")
    .group("/auth", app => {
        return app
            .get("/", () => "Hi")
            .post("/sign-in", ({ body }) => body)
            .put("/sign-up", ({ body }) => body)
    })
    .listen(3000)

Schema

Enforce a data type of a route

See Validation

import { Elysia, t } from 'elysia'

new Elysia()
    .post('/mirror', ({ body: { username } }) => username, {
        body: t.Object({
            username: t.String(),
            password: t.String()
        })
    })
    .listen(3000)

Lifecycle Hook

Intercept an Elysia event in order

See Lifecycle

import { Elysia, t } from 'elysia'

new Elysia()
    .onRequest(() => {
        console.log('On request')
    })
    .on('beforeHandle', () => {
        console.log('Before handle')
    })
    .post('/mirror', ({ body }) => body, {
        body: t.Object({
            username: t.String(),
            password: t.String()
        }),
        afterHandle: () => {
            console.log("After handle")
        }
    })
    .listen(3000)

Guard

Enforce a data type of sub routes

See Scope

import { Elysia, t } from 'elysia'

new Elysia()
    .guard({
        response: t.String()
    }, (app) => app
        .get('/', () => 'Hi')
        // Invalid: will throws error, and TypeScript will report error
        .get('/invalid', () => 1)
Argument of type '() => number' is not assignable to parameter of type 'InlineHandler<MergeSchema<UnwrapRoute<InputSchema<never>, TModule<{}, {}>, "/invalid">, MergeSchema<{}, MergeSchema<{}, { body: unknown; headers: unknown; query: unknown; params: {}; cookie: unknown; response: { 200: string; }; }, "">, "">, "">, { ...; } & { ...; }, "/invalid">'.
  Type '() => number' is not assignable to type '(context: { body: unknown; query: Record<string, string | undefined>; params: {}; headers: Record<string, string | undefined>; cookie: Record<string, Cookie<string | undefined>>; ... 8 more ...; error: <const Code extends "OK" | 200, const T extends Code extends 200 ? { ...; }[Code] : Code extends "Continue" | ... 5...'.
    Type 'number' is not assignable to type 'Response | MaybePromise<string | { 200: string; } | ElysiaCustomStatusResponse<200, string, 200>>'.
    )
    .listen(3000)

Customize context

Add custom variable to route context

See Context

import { Elysia } from 'elysia'

new Elysia()
    .state('version', 1)
    .decorate('getDate', () => Date.now())
    .get('/version', ({
        getDate,
        store: { version }
    }) => `${version} ${getDate()}`)
    .listen(3000)

Redirect

Redirect a response

See Handler

import { Elysia } from 'elysia'

new Elysia()
    .get('/', () => 'hi')
    .get('/redirect', ({ redirect }) => {
        return redirect('/')
    })
    .listen(3000)

Plugin

Create a separate instance

See Plugin

import { Elysia } from 'elysia'

const plugin = new Elysia()
    .state('plugin-version', 1)
    .get('/hi', () => 'hi')

new Elysia()
    .use(plugin)
    .get('/version', ({ store }) => store['plugin-version'])
    .listen(3000)

Web Socket

Create a realtime connection using Web Socket

See Web Socket

import { Elysia } from 'elysia'

new Elysia()
    .ws('/ping', {
        message(ws, message) {
            ws.send('hello ' + message)
        }
    })
    .listen(3000)

OpenAPI documentation

Create interactive documentation using Scalar (or optionally Swagger)

See swagger

import { Elysia } from 'elysia'
import { swagger } from '@elysiajs/swagger'

const app = new Elysia()
    .use(swagger())
    .listen(3000)

console.log(`View documentation at "${app.server!.url}swagger" in your browser`);

Unit Test

Write a unit test of your Elysia app

See Unit Test

// test/index.test.ts
import { describe, expect, it } from 'bun:test'
import { Elysia } from 'elysia'

describe('Elysia', () => {
    it('return a response', async () => {
        const app = new Elysia().get('/', () => 'hi')

        const response = await app
            .handle(new Request('http://localhost/'))
            .then((res) => res.text())

        expect(response).toBe('hi')
    })
})

Custom body parser

Create custom logic for parsing body

See Parse

import { Elysia } from 'elysia'

new Elysia()
    .onParse(({ request, contentType }) => {
        if (contentType === 'application/custom-type')
            return request.text()
    })

GraphQL

Create a custom GraphQL server using GraphQL Yoga or Apollo

See GraphQL Yoga

import { Elysia } from 'elysia'
import { yoga } from '@elysiajs/graphql-yoga'

const app = new Elysia()
    .use(
        yoga({
            typeDefs: /* GraphQL */`
                type Query {
                    hi: String
                }
            `,
            resolvers: {
                Query: {
                    hi: () => 'Hello from Elysia'
                }
            }
        })
    )
    .listen(3000)