Error handling

error is called when an error is thrown.

It accepts context similar to a handler, with an error property containing the thrown error. Use instanceof to check its class.

import { Elysia, NotFound } from 'elysia'

new Elysia()
  .onError(({ error, status }) => {
    if(error instanceof NotFound)
      return 'uhe~ are you lost?'

    return status(418, "My bad! But I'm cute so you'll forgive me, right?")
  })
  .get('/', () => 'ok')
  .listen(3000)

You can return a status to override the default error status.

Custom error

import { Elysia } from 'elysia'

class NicheError extends Error {
  constructor(message: string) {
    super(message)
  }
}

new Elysia()
  .onError(NicheError, ({ error, status }) => {
    // Typed as NicheError
    console.log(error)

    return status(418, "We have no idea how you got here")
  })
  .get('/', () => {
        throw new NicheError('Custom error message')
  })
  .listen(3000)

The handler receives an error typed as NicheError, so its properties are available with autocomplete.

Error status code

You can also provide a custom status code by adding a status property to class:

import { Elysia } from 'elysia'

class NicheError extends Error {
  status = 418

  constructor(message: string) {
    super(message)
  }
}

Elysia will use this status code if the error is thrown, see Custom status code.

Error response

Return a response from the class handler to choose the body and status:

import { Elysia } from 'elysia'

class NicheError extends Error {
  status = 418
}

new Elysia()
  .onError(NicheError, ({ error, status }) =>
    status(error.status, { message: error.message })
  )
  .get('/', () => {
    throw new NicheError('Custom error message')
  })

See Class error handlers.

Assignment

Let’s try to extend Elysia’s context.

Assignments

0 of 2 assignments passed

Your own 404
Not passed yet
Let's override a default 404 response your own
Your custom error
Not passed yet
Let's define your own custom error, throw it in GET "/" endpoint, and return a status 418

Handle the NotFound class to override the 404 response.
Handle YourError and return its 418 status.

import { Elysia, NotFound } from 'elysia'

class YourError extends Error {
  status = 418

  constructor(message: string) {
    super(message)
  }
}

new Elysia()
  .onError(NotFound, () => 'Hi there')
  .onError(YourError, ({ error, status }) => status(error.status, error.message))
  .get('/', () => {
    throw new YourError("A")
  })
  .listen(3000)

One sec, warming things up…

Your own 404

Your custom error