Introduction

Elysia.js is a fast, and friendly Bun web framework.

Pronounce as "eh-LIHZ-iy-ah"・エリシア・ เอลิเซีย

Building on top of 3 philosophies:

Performance
- You shall not worry about the underlying performance
Simplicity
- Simple building blocks to create an abstraction, not repeating yourself
Flexibility
- You shall be able to customize most of the library to fits your need

Designed with TypeScript in mind, you don't need to understand TypeScript to take advantage of Elysia. The library understands what you want and automatically infers the type from your code.

Take a look at this:

typescript

new Elysia()
    .get('/id/:id', (({ params: { id }}) => id))
    .listen(8080)

new Elysia()
    .get('/id/:id', (({ params: { id }}) => id))
    .listen(8080)

Elysia understands that you want a path parameter name id. The library then registers id as a type in params.

You can define a custom type for many things, for example, an incoming request's body.

typescript

import { Elysia, t } from 'elysia'

new Elysia()
    .post('/sign-in', ({ body }) => signIn(body), {
        body: t.Object({
            username: t.String(),
            password: t.String()
        })
    })
    .listen(8080)

import { Elysia, t } from 'elysia'

new Elysia()
    .post('/sign-in', ({ body }) => signIn(body), {
        body: t.Object({
            username: t.String(),
            password: t.String()
        })
    })
    .listen(8080)

You explicitly tell Elysia that the incoming request body is expected to have a structure as you define it.

Elysia then infers the type from the code you write. Validate the body from the incoming request to ensure the type safety.

Then with plugins, Elysia can instantly generate API documentation with Swagger with a single line of code.

typescript

import { Elysia, t } from 'elysia'
import { swagger } from '@elysiajs/swagger'

new Elysia()
    .use(swagger())
    .post('/sign-in', ({ body }) => signIn(body), {
        body: t.Object({
            username: t.String(),
            password: t.String()
        })
    })
    .listen(8080)

import { Elysia, t } from 'elysia'
import { swagger } from '@elysiajs/swagger'

new Elysia()
    .use(swagger())
    .post('/sign-in', ({ body }) => signIn(body), {
        body: t.Object({
            username: t.String(),
            password: t.String()
        })
    })
    .listen(8080)

And finally, you can create a fully type-safe client for consuming Elysia API with Eden (optional).

typescript

// server.ts
import { Elysia, t } from 'elysia'
import { swagger } from '@elysiajs/swagger'

const app = new Elysia()
    .use(swagger())
    .post('/sign-in', ({ body }) => signIn(body), {
        body: t.Object({
            username: t.String(),
            password: t.String()
        })
    })
    .listen(8080)

export type App = typeof app

// server.ts
import { Elysia, t } from 'elysia'
import { swagger } from '@elysiajs/swagger'

const app = new Elysia()
    .use(swagger())
    .post('/sign-in', ({ body }) => signIn(body), {
        body: t.Object({
            username: t.String(),
            password: t.String()
        })
    })
    .listen(8080)

export type App = typeof app

And on the client:

typescript

// client.ts
import { edenTreaty } from '@elysia/eden'
import type { Server } from './server'

const app = edenTreaty<Server>('http://localhost:8080')

app.signIn.post({
    username: 'saltyaom',
    password: 12345678
}).then(console.log)

// client.ts
import { edenTreaty } from '@elysia/eden'
import type { Server } from './server'

const app = edenTreaty<Server>('http://localhost:8080')

app.signIn.post({
    username: 'saltyaom',
    password: 12345678
}).then(console.log)

Creating a single source of truth for your data structure, eliminating any possible type conflict between TypeScript, actual requests via validation, API documentation, and frontend client.

Ensure that nothing went wrong in development, migration, and production.

Introduction ​

Introduction