Elysia.js

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Handler ​

For routing is to tell which function to return a response to.

The function for returning a Response is Handler.

Handler is a callback function which accept Context, helping you access powerful API for accessing data and modifying the response.

The params from the previous example also come from Handler

typescript
// Structure
app.get(path, handler, hook?)

// Usage
app.get('/id/:id', (context) => context.params.id)

// Structure
app.get(path, handler, hook?)

// Usage
app.get('/id/:id', (context) => context.params.id)

Context ​

Context's properties consists of

  • request: Raw Request for accessing data as web standard type
  • body: Body which come with the request
  • query: Parsed path query as a simple object
  • params: Path parameters as a simple object
  • store: A global mutable store for Elysia instance
  • set: Response representation
    • status: response status
    • headers: response headers
    • redirect: redirect to new path

And a few helper methods for convenient usage:

  • status: Function to set HTTP response status code
  • redirect: Function to redirect to different path
  • setHeader: Syntax sugar for setting specific header value

For both context, you can easily access in Handler function:

typescript
app.post('/', ({ body, set }) => {
    const signed = signIn(body)
    
    if(signed)
        return 'Welcome back'
    else {
        set.status = 403
        return 'Invalid username or password'
    }
})

app.post('/', ({ body, set }) => {
    const signed = signIn(body)
    
    if(signed)
        return 'Welcome back'
    else {
        set.status = 403
        return 'Invalid username or password'
    }
})

TIP

Elysia encourages object destructuring, but set is an exception. As destructured primitive value is not linked to the object, in order to make set work properly, we need to use set.value

Response ​

Returning value from Handler, Elysia will try to map returned value into Response.

For eaxmple, to return an object, you should stringify the content first and then set response header of Content-Type to application/json.

Which look something like this:

typescript
new Response(JSON.stringify({
    'vtuber': [
        'Shirakami Fubuki',
        'Inugami Korone'
    ]
}, {
    headers: {
        'Content-Type': 'application/json'
    }
})

new Response(JSON.stringify({
    'vtuber': [
        'Shirakami Fubuki',
        'Inugami Korone'
    ]
}, {
    headers: {
        'Content-Type': 'application/json'
    }
})

But Elysia handle that for you.

You simply return an object, and Elysia will map your value to a correct response for you.

typescript
app.get('/', () => ({
    'vtuber': [
        'Shirakami Fubuki',
        'Inugami Korone'
    ]
}))

app.get('/', () => ({
    'vtuber': [
        'Shirakami Fubuki',
        'Inugami Korone'
    ]
}))

Ofcourse, as Elysia map the value to Response.

But you can also return a Response if you really want to.

typescript
app.get('/', () => new Response(
    JSON.stringify({
        'vtuber': [
            'Shirakami Fubuki',
            'Inugami Korone'
        ]
    }, {
        headers: {
            'Content-Type': 'application/json'
        }
    })
)

app.get('/', () => new Response(
    JSON.stringify({
        'vtuber': [
            'Shirakami Fubuki',
            'Inugami Korone'
        ]
    }, {
        headers: {
            'Content-Type': 'application/json'
        }
    })
)