Astro.locals is not serializable

Deprecated

This error is from an older version of Astro and is no longer in use. If you are unable to upgrade your project to a more recent version, then you can consult unmaintained snapshots of older documentation for assistance.

LocalsNotSerializable: The information stored in Astro.locals for the path “HREF” is not serializable. Make sure you store only serializable data. (E03034)

What went wrong?

Section titled What went wrong?

Thrown in development mode when a user attempts to store something that is not serializable in locals.

For example:

import {defineMiddleware} from "astro/middleware";
export const onRequest = defineMiddleware((context, next) => {
  context.locals = {
    foo() {
      alert("Hello world!")
    }
  };
  return next();
});