Response

Once the fetch method is called, Eden Treaty returns a Promise containing an object with the following properties:

• data - returned value of the response (2xx)
• error - returned value from the response (>= 3xx)
• response Response - Web Standard Response class
• status number - HTTP status code
• headers FetchRequestInit['headers'] - response headers

Once returned, you must provide error handling to ensure that the response data value is unwrapped, otherwise the value will be nullable. Elysia provides a error() helper function to handle the error, and Eden will provide type narrowing for the error value.

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

const app = new Elysia()
    .post('/user', ({ body: { name }, status }) => {
        if(name === 'Otto') return status(400)

        return name
    }, {
        body: t.Object({
            name: t.String()
        })
    })
    .listen(3000)

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

const submit = async (name: string) => {
    const { data, error } = await api.user.post({
        name
    })

    // type: string | null
    console.log(data)

    if (error)
        switch(error.status) {
            case 400:
                // Error type will be narrow down
                throw error.value

            default:
                throw error.value
        }

    // Once the error is handled, type will be unwrapped
    // type: string
    return data
}

By default, Elysia infers error and response types to TypeScript automatically, and Eden will be providing auto-completion and type narrowing for accurate behavior.

::: tip If the server responds with an HTTP status >= 300, then the value will always be null, and error will have a returned value instead.

Otherwise, response will be passed to data. :::

Stream response

Eden will interpret a stream response or Server-Sent Events as AsyncGenerator allowing us to use for await loop to consume the stream.

::: code-group

import { Elysia } from 'elysia'
import { treaty } from '@elysiajs/eden'

const app = new Elysia()
	.get('/ok', function* () {
		yield 1
		yield 2
		yield 3
	})

const { data, error } = await treaty(app).ok.get()
if (error) throw error

for await (const chunk of data)
	console.log(chunk)
               // ^?

import { Elysia, sse } from 'elysia'
import { treaty } from '@elysiajs/eden'

const app = new Elysia()
	.get('/ok', function* () {
		yield sse({
			event: 'message',
			data: 1
		})
		yield sse({
			event: 'message',
			data: 2
		})
		yield sse({
			event: 'end'
		})
	})

const { data, error } = await treaty(app).ok.get()
if (error) throw error

for await (const chunk of data)
	console.log(chunk)
               // ^?







//

:::

Utility type

Eden Treaty provides a utility type Treaty.Data<T> and Treaty.Error<T> to extract the data and error type from the response.

import { Elysia, t } from 'elysia'

import { treaty, Treaty } from '@elysiajs/eden'

const app = new Elysia()
	.post('/user', ({ body: { name }, status }) => {
		if(name === 'Otto') return status(400)

		return name
	}, {
		body: t.Object({
			name: t.String()
		})
	})
	.listen(3000)

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

type UserData = Treaty.Data<typeof api.user.post>
//     ^?


// Alternatively you can also pass a response
const response = await api.user.post({
	name: 'Saltyaom'
})

type UserDataFromResponse = Treaty.Data<typeof response>
//     ^?



type UserError = Treaty.Error<typeof api.user.post>
//     ^?












//