Error Handling

Hedystia provides multiple mechanisms to handle errors — both expected errors (validation failures, business logic errors) and unexpected ones (runtime exceptions).

Throwing Errors from a Handler

Every handler context includes an error helper that throws a typed HTTP error:

import Hedystia, { h } from 'hedystia'

const app = new Hedystia()
  .get('/error', ({ error }) => {
    return error(418, "I'm a teapot")
  })

Calling error() throws internally. The framework catches it and serializes it as:

Response

{
  "message": "User not found",
  "code": 404
}

Typed Error Responses

Declare the shape of your error response with the error schema field. This drives client-side type inference.

app.get(
  '/users/:id',
  ({ params, error }) => {
    if (params.id === 0) error(404, 'User not found')
    return { id: params.id }
  },
  {
    params: h.object({ id: h.number().coerce() }),
    response: h.object({ id: h.number() }),
    error: h.object({
      message: h.string(),
      code: h.number(),
    }),
  }
)

On the client side:

import { createClient } from '@hedystia/client'
import type { app } from './server'

const client = createClient<typeof app>('http://localhost:3000')

const { data, error } = await client.users.id(0).get()
if (error) {
  console.log(error.message)  // typed as string
  console.log(error.code)     // typed as number
}

Static Error Constructor

You can also use the static Hedystia.error() method from outside a handler context:

import Hedystia from 'hedystia'

function requireAuth(token?: string) {
  if (!token) {
    throw { statusCode: 401, message: 'Missing authorization token' }
  }
}

Global Error Handler

Use onError to catch all uncaught errors and return a custom response:

const app = new Hedystia()
  .onError((error, ctx) => {
    if (error.statusCode === 401) {
      return { error: 'You shall not pass' }
    }

    const status = error.statusCode ?? 500
    const message = error.message ?? 'Something went wrong'

    return Response.json({ error: message, status }, { status })
  })
  .get('/crash', () => {
    throw new Error('Unexpected failure')
  })
  .listen(3000)

Validation Errors

When request data fails schema validation, Hedystia automatically responds with a 400 error before invoking your handler:

Scenario	Status
Invalid path params	400
Invalid query params	400
Invalid request body	400
Invalid headers	400

You do not need to handle validation errors manually.

Subscription Errors

In subscriptions, use sendError to push a typed error to the client without closing the connection:

app.subscription(
  '/notifications/:userId',
  async ({ params, sendData, sendError }) => {
    if (params.userId === 'banned') {
      sendError({ reason: 'Account suspended', severity: 'high' })
      return
    }
    sendData({ message: 'Welcome back!', timestamp: Date.now() })
  },
  {
    params: h.object({ userId: h.string() }),
    data: h.object({
      message: h.string(),
      timestamp: h.number(),
    }),
    error: h.object({
      reason: h.string(),
      severity: h.options(h.literal('low'), h.literal('high')),
    }),
  }
)

CORS and Preflight

CORS errors are handled automatically when CORS is enabled:

const app = new Hedystia({ cors: true })

Or with fine-grained control:

const app = new Hedystia({
  cors: {
    origin: ['https://app.example.com'],
    credentials: true,
    methods: ['GET', 'POST', 'PUT', 'DELETE'],
  },
})

Preflight (OPTIONS) requests are handled automatically — no extra routes needed.