When object signatures match exactly, TypeScript issues a warning

I am facing an issue with typescript while trying to use my own custom type from express' types.

When I attempt to pass 'Request<ParamsDictionary, any, any, ParsedQs, Record<string, any>>' as a parameter of type 'Context', I get an error saying it is not assignable.

The error mentioned that the property 'req' is missing in type 'Request<ParamsDictionary, any, any, ParsedQs, Record<string, any>>', but it's required in type 'Context'.

Although the type signatures seem identical, I'm struggling to figure out what mistake I'm making here. How can I successfully pass req and res to the function getStatus? Routes.ts

import getStatus from "../routes/status";
 
export default function routes({ app }: Context): void {  
  app.get("/_status", ({ req, res }: Context) => getStatus(req, res));  
} // digging into issues here                                    ^^^^^^^^

Status.ts

import { Context } from "../../utils/Context";
import express from "express";

export default async function getStatus({req}: Context, { res }: Context): Promise<Express.Response> {
//....
}

Context.ts

import { Request, Response, Application } from "express";
export type Context = {
  req: Request;
  res: Response;
  app: Application;
};

Answer №1

One issue to address is the double destructuring happening in your code. The anonymous function parameter already extracts the req and res from Context, but then these fields are passed to getStatus which expects two Context parameters for extraction of req and res again.

To resolve this, it might be best to change the signature of getStatus so that Request and Response are the types of the two parameters.

export default async function getStatus(req: Request, res: Response): Promise<Express.Response> {
   //....
}

Alternatively, you could simply pass context as one parameter.

app.get("/_status", getStatus)
export default async function getStatus({ req, res }: Context): Promise<Express.Response> {
   //....
}

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