Elysia/Eden Type Inference Issue: Response Inferred as any

[amir-reza-bijandi]

I just recently started using Elysia, and I've encountered a problem that I can't wrap my head around! In the example below, when I try to use Eden, the response type is inferred as any (animeList and data variables):

[mal/index.ts]:

import Elysia from 'elysia';
import { MalModel } from './model';
import { Mal } from './service';

export const malRoute = new Elysia({ prefix: '/mal' }).get('/', async ({ query }) => await Mal.search(query), {
  query: MalModel.searchQuery,
});

[add-anime-modal.svelte]:

	let q = $state('');
	let animeList = $state<Treaty.Data<typeof api.mal.get> | null>(null);
	const handleSubmit: FormEventHandler<HTMLFormElement> = async () => {
		const { data, error } = await api.mal.get({
			query: {
				q
			}
		});
		animeList = data;
	};

The Fix

I was stuck on this issue for a while, and I was trying to figure out what I did wrong, but all I had to do was to make the following change (explicitly casting the return value):

import Elysia from 'elysia';
import { MalModel } from './model';
import { Mal } from './service';
import type { Anime } from 'jikan4.js';

export const malRoute = new Elysia({ prefix: '/mal' }).get(
  '/',
  async ({ query }) => (await Mal.search(query)) as Anime[],
  {
    query: MalModel.searchQuery,
  }
);

Seeking Explanation

Is there an explanation for this behavior? Why was the return type not automatically inferred from the await Mal.search(query) result, and why was the explicit as Anime[] cast necessary for Eden to correctly infer the type?

This is the GitHub repository if you want to play around with the code: https://github.com/amir-reza-bijandi/anime

[mtt-artis]

Hi 👋

seems more like a tsconfig or ts export problem to me.

apps/admin-server

packages/admin-api-type

I'm not a TS expert but one solution could be generating .d.ts files and expose them in your package.json

Also, be careful, as the Anime is a class with methods that you cannot call on the client side (even if the type says so).

[amir-reza-bijandi]

Thanks for the workaround, but if I plan to use Elysia at work, I need to have a good understanding of what works and what doesn't. I would much rather have an explanation of why the inference does not work here and what's causing it!