Middlewares should accept arguments

[luciorubeens]

Hey there!

Is there a way in the current version to pass arguments to middlewares?

If not, is this metadata field in the Effect type useful for it?

[JozefFlakus]

Hi,

Sure thing, you can pass as many arguments as you want to middlewares. Just wrap them inside a function with parameters and return an Effect:

export const foo = (bar: string): Effect<HttpRequest> => request$ => request$
  .pipe(
    tap(() => console.log(bar)),
  );

then in middlewares definition:

const middlewares = [
  logger$,
  bodyParser$,
  foo('test'),
];

[luciorubeens]

@JozefFlakus Makes sense. Thank you! 👍

Can you explain how this metadata will be used?

[JozefFlakus]

I'm glad that I've helped! :)

Right now metadata field is used only for error middlewares. In this case the so called metadata field will contain throwed error object which you can use for error handling-related logic.

const error$: Effect<EffectResponse, ThrowedError> = (request$, response, error) => request$
  .pipe(
    map(req => ({
      status: // ...
      body:  // ...
    }),
  );

But who knows, maybe in the future we will be able to use this parameter in different way.