Responses & Errors

Moost converts your handler's return value into an HTTP response automatically. This page covers response formats, status codes, headers, cookies, error handling, and raw response access.

Automatic response handling

The return value of a handler determines the response:

Return type	Content-Type	Behavior
string	text/plain	Sent as plain text
object / array	application/json	JSON-serialized
boolean	application/json	JSON-serialized
ReadableStream	streamed	Piped to response
fetch Response	forwarded	Status, headers, and body preserved

content-length is set automatically for non-streamed responses.

Setting status codes

Static — @SetStatus

When the status code is always the same:

import { Post, SetStatus } from '@moostjs/event-http'
import { Controller } from 'moost'

@Controller('users')
export class UserController {
    @Post('')
    @SetStatus(201)
    create() {
        return { created: true } // always responds with 201
    }
}

By default, @SetStatus won't override a status code that was already set (e.g., by an error). Pass { force: true } to always override:

@SetStatus(200, { force: true })

Dynamic — @StatusRef

When the status code depends on runtime logic:

import { Get, StatusRef } from '@moostjs/event-http'
import type { TStatusRef } from '@moostjs/event-http'

@Get('process')
process(@StatusRef() status: TStatusRef) {
    if (someCondition) {
        status.value = 202 // Accepted
        return { status: 'processing' }
    }
    return { status: 'done' } // default 200
}

Setting headers

Static — @SetHeader

import { Get, SetHeader } from '@moostjs/event-http'

@Get('test')
@SetHeader('x-powered-by', 'moost')
@SetHeader('cache-control', 'no-store')
test() {
    return 'ok'
}

@SetHeader supports additional options:

// Only set this header when the response status is 400
@SetHeader('content-type', 'text/plain', { status: 400 })

// Override even if the header was already set
@SetHeader('x-custom', 'value', { force: true })

// Set on both success and error responses
@SetHeader('x-request-id', 'abc', { when: 'always' })

// Set only on error responses
@SetHeader('x-error', 'true', { when: 'error' })

Dynamic — @HeaderRef

import { Get, HeaderRef } from '@moostjs/event-http'
import type { THeaderRef } from '@moostjs/event-http'

@Get('test')
test(@HeaderRef('x-custom') header: THeaderRef) {
    header.value = `generated-${Date.now()}`
    return 'ok'
}

Setting cookies

Static — @SetCookie

import { Get, SetCookie } from '@moostjs/event-http'

@Get('login')
@SetCookie('session', 'abc123', { maxAge: '1h', httpOnly: true })
login() {
    return { ok: true }
}

INFO

@SetCookie won't overwrite a cookie that was already set in the response. This prevents accidental overwrites when multiple decorators or interceptors set the same cookie.

Dynamic — @CookieRef

import { Post, CookieRef } from '@moostjs/event-http'
import type { TCookieRef } from '@moostjs/event-http'

@Post('login')
login(@CookieRef('session') cookie: TCookieRef) {
    const token = generateToken()
    cookie.value = token
    cookie.attrs = { maxAge: '1h', httpOnly: true, secure: true }
    return { ok: true }
}

Error handling

Unhandled errors

Any uncaught exception becomes an HTTP 500 response:

@Get('fail')
fail() {
    throw new Error('Something broke')
    // → 500 Internal Server Error
}

HttpError

Use HttpError to throw errors with specific HTTP status codes:

import { HttpError } from '@moostjs/event-http'

@Get('secret')
secret() {
    throw new HttpError(403, 'Access denied')
    // → 403 Forbidden with message "Access denied"
}

Detailed error responses

Pass an object for structured error bodies:

throw new HttpError(422, {
    message: 'Validation failed',
    statusCode: 422,
    errors: [
        { field: 'email', message: 'Invalid email format' },
        { field: 'age', message: 'Must be a positive number' },
    ],
})

The response format (JSON or HTML) adapts based on the request's Accept header.

Error interceptors

For centralized error handling across multiple handlers, see Interceptors.

Raw response

For full control over the response, use @Res() to access the raw ServerResponse. When you do, the framework does not process the handler's return value — you're responsible for the entire response.

import { Get, Res } from '@moostjs/event-http'
import type { ServerResponse } from 'http'

@Get('raw')
raw(@Res() res: ServerResponse) {
    res.writeHead(200, { 'content-type': 'text/plain' })
    res.end('Manual response')
}

Passthrough mode

If you need the raw response object but still want the framework to process your return value, use { passthrough: true }:

@Get('hybrid')
hybrid(@Res({ passthrough: true }) res: ServerResponse) {
    res.setHeader('x-custom', 'value')
    return { data: 'processed by framework' } // framework handles this
}