What is context.data in pages functions

[safa]

Can anyone please explain what is context.data in pages functions and how it can be used?

Documentation is at: API reference · Cloudflare Pages docs

[cherryjimbo]

It’s an arbitrary object you can attach data to that will persist during the request. The most common use-cases are for middleware that handles auth and may need to set context.data.username or similar.

[safa]

Thank you for the answer. However, this does not work.

I added data to context.data in my middleware. I checked data was there with a console.log.
Then I called context.next() to invoke my function and did console.log on context.data. It was empty. Is this a bug or do I have to do something special to make sure data is passed from my middleware to the api?

Note, I’m using Typescript.

[cherryjimbo]

Can you share a minimal reproduction? Did you await context.next()?

It should be working fine based on your description.

[safa]

Middleware Function: authenticate

async function authenticate(context) {
  console.log('authenticating');

  ... code -- redacted ...

      context.data = {lower:{data:"some data"}};
      console.log('middleware context');
      console.log(context.data);
      return await context.next();
    }
  }
}

Middleware function: error handler

async function handleErrors(context) {
  console.log('handling errors');
  try {
    return await context.next();
  } catch (err) { // uncaught exceptions
    console.log('uncaught error');
    console.log(err);
    return new Response(
      'Uncaught Server Error', 
      { status: TYPES.HTTP_ERROR.INTERNAL_SERVER_ERROR });
  }
}

// Chained middleware: handleErrors runs first
export const onRequest = [handleErrors, authenticate];

Called function: getInfo

export async function onRequest( context ) {
  console.log('getInfo');
  console.log(context.data);

  return new Response(`getInfo`);
}

Result

handling errors
authenticating
middleware context
{ lower: { data: 'some data' } }
getInfo
{}

Please Note: Using Typescript

[cherryjimbo]

Hmm, it seems I’m able to reproduce this too. Let me dig in a little and get this in front of the right people if needed.

[cherryjimbo]

Turns out this is a bug when you override context.data in its entirety. I’ve reproduced and reported here:

🐛 BUG: Pages middleware context.data not persisted if overwritten

To work around it, avoid setting context.data entirely and instead do things like context.data.lower = {...}.

[safa]

Thank you. That solved it.