Loaders

Loaders are useful for one-time loading of data from the server to the client and can only be used in routes in your app directory.

For a more general purpose data solution, see load and query.

Loaders run on the server, either once during build-time for normal routes, or once on each request for +ssr routes.

Loaders and their imports are removed from client bundles, so you can access private information from within the loader. The data returned from the loader will be passed to the client, and so should be clear of private information. To access the loader data on the client, you must use the useLoader hook:

import { useLoader } from 'one'

export async function loader() {
  return {
    user: 'tamagui'
  }
}

export default function HomePage() {
  const data = useLoader(loader)
  
  return (
    <p>
      {data.user}
    </p>
  )
}

The useLoader hook is automatically type safe.

Loader arguments

Loaders receive a single argument object:

params

The params key will provide values from any dynamic route segments:

app/user/[id].tsx
export async function loader({ params }) {
  // for route /user/jamon params.id is a string "jamon"
  const user = await getUser(params.id)
  
  return {
    greet: `Hello ${user.name}`
  }
}

path

The path key is the fully resolved pathname:

app/user/[id].tsx
export async function loader({ path }) {
  // if the route is /user/123 then path is "/user/123"
}

Accepted Return Types

Most JavaScript values, including primitives and objects, will be converted to JSON.

You may also return a Response:

export async function loader({ params: { id } }) {
  const user = await db.users.findOne({ id })
  const body = JSON.stringify(user)
  return new Response(body, {
    headers: {
      'Content-Type': 'application/json',
    },
  })
}

Throwing a Response

A final handy pattern for loaders is throwing a response to end it early:

export async function loader({ params: { id } }) {
  const user = await db.users.findOne({ id })

  if (!user) {
    throw Response.error()
  }
  
  // ... rest of function
}

You can combine this with the redirect utility function:

import { redirect } from 'one'

export async function loader({ params: { id } }) {
  const user = await db.users.findOne({ id })

  if (!user) {
    throw redirect('/login')
  }

  // ... rest of function
}

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