Life Cycle

It's recommended that you have read Essential life-cycle for better understanding of Elysia's Life Cycle.

Life Cycle allows us to intercept an important event at the predefined point allowing us to customize the behavior of our server as needed.

Elysia's Life Cycle event can be illustrated as the following.

Below are the request life cycle available in Elysia:

Request

Notify new event is received

Parse

Parse body into Context.body

Transform

Modify Context before validation

Before Handle

Custom validation before route handler

After Handle

Transform returned value into a new value

Map Response

Map returned value into a response

On Error

Capture error when thrown

On Response

Executed after response sent to the client

Trace

Audit and capture timespan of each event

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Every life-cycle could be apply at both:

1. Local Hook (route)
2. Global Hook

Local Hook

The local hook is executed on a specific route.

To use a local hook, you can inline hook into a route handler:

import { Elysia } from 'elysia'
import { isHtml } from '@elysiajs/html'

new Elysia()
    .get('/', () => '<h1>Hello World</h1>', {
        afterHandle({ response, set }) {
            if (isHtml(response))
                set.headers['Content-Type'] = 'text/html; charset=utf8'
        }
    })
    .get('/hi', () => '<h1>Hello World</h1>')
    .listen(3000)

Global Hook

Register hook into every handler that came after.

To add a global hook, you can use .on followed by a life cycle event in camelCase:

import { Elysia } from 'elysia'
import { isHtml } from '@elysiajs/html'

new Elysia()
    .get('/none', () => '<h1>Hello World</h1>')
    .onAfterHandle(({ response, set }) => {
        if (isHtml(response))
            set.headers['Content-Type'] = 'text/html; charset=utf8'
    })
    .get('/', () => '<h1>Hello World</h1>')
    .get('/hi', () => '<h1>Hello World</h1>')
    .listen(3000)

Events from other plugins are also applied to the route so the order of code is important.