Handler and Context ​

Handler - a resource or a route function to send data back to client.

ts
import { Elysia } from 'elysia'

new Elysia()
    // `() => 'hello world'` is a handler
    .get('/', () => 'hello world')
    .listen(3000)

A handler can also be a literal value, see Handler

ts
import { Elysia } from 'elysia'

new Elysia()
    // `'hello world'` is a handler
    .get('/', 'hello world')
    .listen(3000)

Using an inline value can be useful for static resource like file.

Context ​

Contains information about each request. It is passed as the only argument of a handler.

typescript
import { 
Elysia
 } from 'elysia'

new 
Elysia
()
	.
get
('/', (
context
) => 
context
.
path
)
            // ^ This is a context

Context stores information about the request like:

  • body - data sent by client to server like form data, JSON payload.
  • query - query string as an object. (Query is extracted from a value after pathname starting from '?' question mark sign)
  • params - Path parameters parsed as object
  • headers - HTTP Header, additional information about the request like "Content-Type".

See Context.

Preview ​

You can preview the result by looking under the editor section.

There should be a tiny navigator on the top left of the preview window.

You can use it to switch between path and method to see the response.

You can also click to edit body, and headers.

Assignment ​

Let's try extracting context parameters:

  1. Create POST endpoint

    Let's create a POST endpoint "/", so we can send a body

  2. Extract Body

    Let's extract a body and return it as `return { body }`

  3. Extract Query

    Let's extract a query and return it as `return { body, query }`

  4. Extract Headers

    Let's extract a header and return it as `return { body, query, headers }`

Show answer
  1. We can extract body, query, and headers from the first value of a callback function.
  2. We can then return them like { body, query, headers }.
typescript
import { Elysia } from 'elysia'

new Elysia()
	.post('/', ({ body, query, headers }) => {
		return {
			query,
			body,
			headers
		}
	})
	.listen(3000)

  • index.ts