Eden Installation

Start by installing Eden on your frontend:

bun add @elysiajs/eden
bun add -d elysia

TIP

Eden needs Elysia to infer utilities type.

Make sure to install Elysia with the version matching on the server.

First, export your existing Elysia server type:

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

const app = new Elysia()
    .get('/', () => 'Hi Elysia')
    .get('/id/:id', ({ params: { id } }) => id)
    .post('/mirror', ({ body }) => body, {
        body: t.Object({
            id: t.Number(),
            name: t.String()
        })
    })
    .listen(3000)

export type App = typeof app 

Then consume the Elysia API on client side:

// client.ts
import { treaty } from '@elysiajs/eden'
import type { App } from './server'

const client = treaty<App>('localhost:3000') 

// response: Hi Elysia
const { data: index } = await client.get()

// response: 1895
const { data: id } = await client.id({ id: 1895 }).get()

// response: { id: 1895, name: 'Skadi' }
const { data: nendoroid } = await client.mirror.post({
    id: 1895,
    name: 'Skadi'
})

client.

Gotcha

Sometimes, Eden may not infer types from Elysia correctly, the following are the most common workarounds to fix Eden type inference.

Type Strict

Make sure to enable strict mode in tsconfig.json

{
  "compilerOptions": {
    "strict": true
  }
}

Unmatch Elysia version

Eden depends on Elysia class to import Elysia instance and infer types correctly.

Make sure that both client and server have the matching Elysia version.

You can check it with npm why command:

npm why elysia

And output should contain only one elysia version on top-level:

[email protected]
node_modules/elysia
  elysia@"1.1.25" from the root project
  peer elysia@">= 1.1.0" from @elysiajs/[email protected]
  node_modules/@elysiajs/html
    dev @elysiajs/html@"1.1.1" from the root project
  peer elysia@">= 1.1.0" from @elysiajs/[email protected]
  node_modules/@elysiajs/opentelemetry
    dev @elysiajs/opentelemetry@"1.1.7" from the root project
  peer elysia@">= 1.1.0" from @elysiajs/[email protected]
  node_modules/@elysiajs/swagger
    dev @elysiajs/swagger@"1.1.6" from the root project
  peer elysia@">= 1.1.0" from @elysiajs/[email protected]
  node_modules/@elysiajs/eden
    dev @elysiajs/eden@"1.1.3" from the root project

TypeScript version

Elysia uses newer features and syntax of TypeScript to infer types in the most performant way. Features like Const Generic and Template Literal are heavily used.

Make sure your client has a minimum TypeScript version if >= 5.0

Method Chaining

To make Eden work, Elysia must use method chaining

Elysia's type system is complex, methods usually introduce a new type to the instance.

Using method chaining will help save that new type reference.

For example:

import { Elysia } from 'elysia'

new Elysia()
    .state('build', 1)
    // Store is strictly typed
    .get('/', ({ store: { build } }) => build)
    .listen(3000)

Using this, state now returns a new ElysiaInstance type, introducing build into store replacing the current one.

Without method chaining, Elysia doesn't save the new type when introduced, leading to no type inference.

import { Elysia } from 'elysia'

const app = new Elysia()

app.state('build', 1)

app.get('/', ({ store: { build } }) => build)
Property 'build' does not exist on type '{}'.

app.listen(3000)

Type Definitions

If you are using a Bun specific feature, like Bun.file or similar API and return it from a handler, you may need to install Bun type definitions to the client as well.

bun add -d @types/bun

Path alias (monorepo)

If you are using path alias in your monorepo, make sure that frontend is able to resolve the path as same as backend.

TIP

Setting up path alias in monorepo is a bit tricky, you can fork our example template: Kozeki Template and modify it to your needs.

For example, if you have the following path alias for your backend in tsconfig.json:

{
  "compilerOptions": {
  	"baseUrl": ".",
	"paths": {
	  "@/*": ["./src/*"]
	}
  }
}

And your backend code is like this:

import { Elysia } from 'elysia'
import { a, b } from '@/controllers'

const app = new Elysia()
	.use(a)
	.use(b)
	.listen(3000)

export type app = typeof app

You must make sure that your frontend code is able to resolve the same path alias. Otherwise, type inference will be resolved as any.

import { treaty } from '@elysiajs/eden'
import type { app } from '@/index'

const client = treaty<app>('localhost:3000')

// This should be able to resolve the same module both frontend and backend, and not `any`
import { a, b } from '@/controllers'

To fix this, you must make sure that path alias is resolved to the same file in both frontend and backend.

So, you must change the path alias in tsconfig.json to:

{
  "compilerOptions": {
  	"baseUrl": ".",
	"paths": {
	  "@/*": ["../apps/backend/src/*"]
	}
  }
}

If configured correctly, you should be able to resolve the same module in both frontend and backend.

// This should be able to resolve the same module both frontend and backend, and not `any`
import { a, b } from '@/controllers'

Scope

We recommended adding a scope prefix for each module in your monorepo to avoid any confusion and conflict that may happen.

{
  "compilerOptions": {
  	"baseUrl": ".",
	"paths": {
	  "@frontend/*": ["./apps/frontend/src/*"],
	  "@backend/*": ["./apps/backend/src/*"]
	}
  }
}

Then, you can import the module like this:

// Should work in both frontend and backend and not return `any`
import { a, b } from '@backend/controllers'

We recommend creating a single tsconfig.json that defines a baseUrl as the root of your repo, provide a path according to the module location, and create a tsconfig.json for each module that inherits the root tsconfig.json which has the path alias.

You may find a working example of in this path alias example repo or Kozeki Template.