Integration with Next.js

With Next.js App Router, we can run Elysia on Next.js routes.

1. Create app/api/[[...slugs]]/route.ts
2. Define an Elysia server
3. Export Elysia.fetch with the name of the HTTP methods you want to use

app/api/[[...slugs]]/route.ts

import { Elysia, t } from 'elysia'

const app = new Elysia({ prefix: '/api' })
    .get('/', 'Hello Nextjs')
    .post('/', ({ body }) => body, {
        body: t.Object({
            name: t.String()
        })
    })

export const GET = app.fetch 
export const POST = app.fetch 

Elysia will work normally because of WinterTC compliance.

You can treat the Elysia server as a normal Next.js API route.

With this approach, you can have co-location of both frontend and backend in a single repository and have End-to-end type safety with Eden with both client-side and server action

pnpm

If you use pnpm, pnpm doesn't auto install peer dependencies by default forcing you to install additional dependencies manually.

pnpm add @sinclair/typebox openapi-types

Prefix

Because our Elysia server is not in the root directory of the app router, you need to annotate the prefix on the Elysia server.

For example, if you place the Elysia server in app/user/[[...slugs]]/route.ts, you need to annotate the prefix as /user on the Elysia server.

app/user/[[...slugs]]/route.ts

import { Elysia, t } from 'elysia'

const app = new Elysia({ prefix: '/user' }) 
	.get('/', 'Hello Nextjs')
    .post('/', ({ body }) => body, {
        body: t.Object({
            name: t.String()
        })
    })

export const GET = app.fetch
export const POST = app.fetch

This will ensure that Elysia routing works properly wherever you place it.

Eden

We can add Eden for end-to-end type safety similar to tRPC.

In this approach, we will use the isomorphic fetch pattern to allow Elysia to:

1. On Server: directly call Elysia without going through the network layer
2. On Client: call Elysia through the network layer

To start, we need to do the following steps:

1. Export Elysia instance

app/api/[[...slugs]]/route.ts

import { Elysia } from 'elysia'

export const app = new Elysia({ prefix: '/api' }) 
	.get('/', 'Hello Nextjs')
	.post(
		'/user',
		({ body }) => body,
		{
			body: treaty.schema('User', {
				name: 'string'
			})
		}
	)

export const GET = app.fetch
export const POST = app.fetch

2. Create a Treaty client with isomorphic approach

lib/eden.ts

import { treaty } from '@elysiajs/eden'
import type { app } from '../app/api/[[...slugs]]/route'

// .api to enter /api prefix
export const api =
  // process is defined on server side and build time
  typeof process !== 'undefined'
    ? treaty(app).api
    : treaty<typeof app>('localhost:3000').api

It's important that you should use typeof process instead of typeof window because window is not defined during build time, causing hydration error.

3. Use the client in both server and client components

app/page.tsx

import { api } from '../lib/eden'

export default async function Page() {
	const message = await api.get()

	return <h1>Hello, {message}</h1>
}

This allows you to have type safety from the frontend to the backend with minimal effort and works with both server and client components, as well as with Incremental Static Regeneration (ISR).

React Query

We can also use React Query to interact with the Elysia server on the client.

src/routes/index.tsx

import { createFileRoute } from '@tanstack/react-router'
import { useQuery } from '@tanstack/react-query'

import { getTreaty } from './api.$'

export const Route = createFileRoute('/a')({
	component: App
})

function App() {
	const { data: response } = useQuery({ 
		queryKey: ['get'], 
		queryFn: () => getTreaty().get() 
	}) 

	return response?.data
}

This can work with any React Query features like caching, pagination, infinite queries, etc.

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Please refer to Next.js Route Handlers for more information.