Before Handle

Execute after validation and before the main route handler.

Designed to provide a custom validation to provide a specific requirement before running the main handler.

If a value is returned, the route handler will be skipped.

It's recommended to use Before Handle in the following situations:

• Restricted access check: authorization, user sign-in
• Custom request requirement over data structure

Example

Below is an example of using the before handle to check for user sign-in.

import { Elysia } from 'elysia'
import { validateSession } from './user'

new Elysia()
    .get('/', () => 'hi', {
        beforeHandle({ set, cookie: { session } }) {
            if (!validateSession(session.value))
                return (set.status = 'Unauthorized')
        }
    })
    .listen(3000)

The response should be listed as follows:

Is signed in	Response
❌	Unauthorized
✅	Hi

Guard

When we need to apply the same before handle to multiple routes, we can use guard to apply the same before handle to multiple routes.

import { Elysia } from 'elysia'
import {
    signUp,
    signIn,
    validateSession,
    isUserExists
} from './user'

new Elysia()
    .guard(
        {
            beforeHandle({ set, cookie: { session } }) {
                if (!validateSession(session.value))
                    return (set.status = 'Unauthorized')
            }
        },
        (app) =>
            app
                .get('/user/:id', ({ body }) => signUp(body))
                .post('/profile', ({ body }) => signIn(body), {
                    beforeHandle: isUserExists
                })
    )
    .get('/', () => 'hi')
    .listen(3000)

Resolve

A "safe" version of derive.

Designed to append new value to context after validation process storing in the same stack as beforeHandle.

Resolve syntax is identical to derive, below is an example of retrieving a bearer header from the Authorization plugin.

import { Elysia, t } from 'elysia'

new Elysia()
    .guard(
        {
            headers: t.Object({
                authorization: t.TemplateLiteral('Bearer ${string}')
            })
        },
        (app) =>
            app
                .resolve(({ headers: { authorization } }) => {
                    return {
                        bearer: authorization.split(' ')[1]
                    }
                })
                .get('/', ({ bearer }) => bearer)
    )
    .listen(3000)

Using resolve and onBeforeHandle is stored in the same queue.

import { Elysia } from 'elysia'

new Elysia()
    .onBeforeHandle(() => {
        console.log(1)
    })
    .resolve(() => {
        console.log(2)

        return {}
    })
    .onBeforeHandle(() => {
        console.log(3)
    })

The console should log as the following:

1
2
3

Same as derive, properties which assigned by resolve is unique and not shared with another request.

Guard resolve

As resolve is not available in local hook, it's recommended to use guard to encapsulate the resolve event.

import { Elysia } from 'elysia'
import { isSignIn, findUserById } from './user'

new Elysia()
    .guard(
        {
            beforeHandle: isSignIn
        },
        (app) =>
            app
                .resolve(({ cookie: { session } }) => ({
                    userId: findUserById(session.value)
                }))
                .get('/profile', ({ userId }) => userId)
    )
    .listen(3000)