How to access the environment variables when using createMiddleware()/createHandler()

[FraBle]

Example use case: configure an API client from environment variables.
For instance, Hono has an env() adapter that makes the environment variables in Cloudflare accessible to a request handler/middleware via the context object.

createMiddleware()/createHandler() do accept parameters that can be passed to the middleware/handler, but expect them to be known at build time (example from the docs). In my use case, I'd like to pass in API client details from the environment, which lives in the context object in Hono, which is only known at runtime.

[magne4000]

An equivalent of Hono env could be a good idea, I need to think about it.

In the mean time, you can perhaps try to give an object with a function as your middleware parameters:

interface Arg {
  getEnv: () => Record<string, string>
}

const contextMiddleware = ((arg) => (request, ctx, runtime) => {
  const env = arg.getEnv();
  // ...
}) satisfies Get<[Arg], UniversalMiddleware>;

[magne4000]

You can also create an env helper like this:

export function env<T extends Record<string, unknown>>(runtime: RuntimeAdapter): T {
  switch (runtime.runtime) {
    case "bun":
    case "node":
    case "edge-light":
      return globalThis?.process?.env as T;
    case "deno":
      // @ts-ignore
      return Deno.env.toObject() as T;
    case "workerd":
      return (runtime.env ?? {}) as T;
    default:
      return {} as T;
  }
}

[magne4000]

env helper available in @universal-middleware/[email protected] (same code as above)