JSONObject-type enforces Index signature on all interfaces used in the defineEventHandler() return statement.

[ArthurMJ96]

The JSONObject-type (here) requires us to add an Index signature to all interfaces used in the defineEventHandler() return statement.
Forcing us to add [key: string]: any; to our Interfaces allows for errors later on.

Example:

interface Product {
  id: string
  name: string
}

export default defineEventHandler(async (_event) => { // Error given at this point (See below)
  const products: Product[] = [] // Pretend we got some products from the database
  return {
    products,
  }
})

# Error
Argument of type '(_event: CompatibilityEvent) => Promise<{ products: Product[]; }>' is not assignable to parameter of type 'EventHandler<H3Response>'.
  Type 'Promise<{ products: Product[]; }>' is not assignable to type 'H3Response'.
    Type 'Promise<{ products: Product[]; }>' is not assignable to type 'Promise<_H3Response>'.
      Type '{ products: Product[]; }' is not assignable to type '_H3Response'.
        Type '{ products: Product[]; }' is not assignable to type 'JSONObject'.
          Property 'products' is incompatible with index signature.
            Type 'Product[]' is not assignable to type 'JSONValue'.
              Type 'Product[]' is not assignable to type 'JSONArray'.
                Type 'Product' is not assignable to type 'JSONValue'.
                  Type 'Product' is not assignable to type 'JSONObject'.
                    Index signature for type 'string' is missing in type 'Product'.ts(2345)

---

This would remove the error on our side. But this doesn't really represent our type and allows for more errors later on.

interface Product {
  [key: string]: any;
  id: string
  name: string
}

[pi0]

Thanks for the report. I think we can keep H3Reponse to simple any (same as JSON.stringify) until finding a reliable way to type-check JSON objects.