Overview
Elysia is a JavaScript HTTP server library that targets the Bun JavaScript runtime.
Elysia is a competitor to Hono. It has slightly better performance than Hono, but only runs in Bun. Both Elysia and Hono are significantly faster that Express.
These notes are currently quite minimal.
See the example Elysia project at elysia-demos.
Context
The Context object that is passed to routes has many properties.
The most useful properties on the Context object related to extracting data from a request are described in the following table. This assumes that the variable c holds a Context object that was passed to a route function. Typically this is destructured in the argument list.
| Action | Code |
|---|---|
| get value of request header | c.headers['some-name'] |
| get value of path parameter | c.params['some-name'] |
| get value of query parameter | c.query['some-name'] |
| get value of text body | const text = c.body; |
| get form data from body | const formData = c.body; |
get property from formData | const value = formData.some-name; |
| get value of JSON body | const object = c.body; |
Elysia determines how to parse request bodies based on the value of the Content-Type request header. See Explicit Body.
The most useful properties on the Context object related to creating a response are described in the following table.
| Action | Code |
|---|---|
| set value of a response header | c.header('Some-Name', 'some value'); |
| set status code | c.status(someCode); |
| return text response | return 'some text'; |
| return JSON response | return someObject; |
| return HTML response | return someJSX; |
| return "Not Found" error | set.status = 404; return 'Not Found'; |
| redirect to another URL | set.redirect = 'someURL' |
Returning JSX that is converted to HTML requires the following setup:
bun add @elysiajs/html- Import with
import {html} from '@elysiajs/html'; - Configure with
app.use(html());