Getting error while using " return res.json({ }) "

[tanmayvaij]

using "express": "^4.21.0",
created this middleware for token verification

import { NextFunction, Request, Response } from "express";
import { JwtPayload, verify } from "jsonwebtoken";

declare global {
  namespace Express {
    interface Request {
      user: JwtPayload;
    }
  }
}

export const tokenVerifier = (
  req: Request,
  res: Response,
  next: NextFunction
) => {
  try {
    const authHeader = req.headers.authorization;

    if (!authHeader)
      return res.json({
        err: "authorization token was not provided",
        isSuccess: false,
      });

    const token = authHeader!.split(" ")[1];

    req.user = verify(
      token,
      process.env.FLEXIBASE_AUTH_SECRET_KEY!
    ) as JwtPayload;

    next();
  } catch (err) {
    return res.json({ isSucess: false, err });
  }
};

D:\Projects\flexibase-auth\node_modules\ts-node\src\index.ts:859
    return new TSError(diagnosticText, diagnosticCodes, diagnostics);
           ^
TSError: ⨯ Unable to compile TypeScript:
src/routers/auth.router.ts:13:38 - error TS2769: No overload matches this call.
  The last overload gave the following error.
    Argument of type '(req: Request, res: Response, next: NextFunction) => Response<any, Record<string, any>> | undefined' is not assignable to parameter of type 'RequestHandlerParams<ParamsDictionary, any, any, ParsedQs, Record<string, any>>'.
      Type '(req: Request, res: Response, next: NextFunction) => Response<any, Record<string, any>> | undefined' is not assignable to type 'RequestHandler<ParamsDictionary, any, any, ParsedQs, Record<string, any>>'.
        Type 'Response<any, Record<string, any>> | undefined' is not assignable to type 'void | Promise<void>'.
          Type 'Response<any, Record<string, any>>' is not assignable to type 'void | Promise<void>'.

13 authRouter.route("/verify-user").get(tokenVerifier, verifyUserController);
                                        ~~~~~~~~~~~~~

  node_modules/@types/express-serve-static-core/index.d.ts:203:5
    203     <
            ~
    204         P = ParamsDictionary,
        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    ...
    212         ...handlers: Array<RequestHandlerParams<P, ResBody, ReqBody, ReqQuery, LocalsObj>>
        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    213     ): T;
        ~~~~~~~~~
    The last overload is declared here.

    at createTSError (D:\Projects\flexibase-auth\node_modules\ts-node\src\index.ts:859:12)
    at reportTSError (D:\Projects\flexibase-auth\node_modules\ts-node\src\index.ts:863:19)
    at getOutput (D:\Projects\flexibase-auth\node_modules\ts-node\src\index.ts:1077:36)
    at Object.compile (D:\Projects\flexibase-auth\node_modules\ts-node\src\index.ts:1433:41)
    at Module.m._compile (D:\Projects\flexibase-auth\node_modules\ts-node\src\index.ts:1617:30)
    at Module._extensions..js (node:internal/modules/cjs/loader:1435:10)
    at Object.require.extensions.<computed> [as .ts] (D:\Projects\flexibase-auth\node_modules\ts-node\src\index.ts:1621:12)
    at Module.load (node:internal/modules/cjs/loader:1207:32)
    at Function.Module._load (node:internal/modules/cjs/loader:1023:12)
    at Module.require (node:internal/modules/cjs/loader:1235:19) {
  diagnosticCodes: [ 2769 ]

i get this err while starting the server

[tanmayvaij]

the problem was in @types/express@5.0.0 , when i used previous version the issue was solved

[brettearle]

EDIT: THIS COMMENT IRRELEVANT

Looking to lend a hand, what help do you want here? More info on the bug, updated types for 5.0, overload that allows res return?
Have only read this issue will dig in some tomorrow

[brettearle]

Q1: is it express intention to not call next and return out of a middleware? Doco is only representative of calling next(), to handle errors out of them it's handed to custom error handler
https://expressjs.com/en/guide/writing-middleware.html

EDIT: BELOW IRRELEVANT
Q2: Should app.{verb} take middle ware before final handler, or are these verb fns meant to be single handler end points?

Note1: I have looked at the types that are throwing in types/express-serve-static-core, they seem to have no changes since v4. This was a quick look.

Will get to more work over the weekend

[brettearle]

It seems that types for 5 are working as intended because next is the intention of middleware instead of returning directly out of them.
This is pending answers from library authors as I don't know the intentions for 5

[brettearle]

Related issue #5987

[DylasX]

Hey @tanmayvaij hope you find well, so basically something that you can do with that version of @types/express@5.0.0 is changing a little bit your approach instead of using return res.json you can use the next approach

export const tokenVerifier =   (
  req: Request,
  res: Response,
  next: NextFunction
): void => {
  try {
    const authHeader = req.headers.authorization;

    if (!authHeader) 
      return next(JSON.stringify({err: "authorization token was not provided",isSucess: false}));

    const token = authHeader!.split(" ")[1];

    req.user = verify(
      token,
      process.env.FLEXIBASE_AUTH_SECRET_KEY!
    ) as JwtPayload;

    next();
  } catch (err) {
    return next(JSON.stringify({ isSucess: false, err }));
  }
};

[DylasX]

This issue is related to this interface in express-serve-static-core

export interface RequestHandler<
    P = ParamsDictionary,
    ResBody = any,
    ReqBody = any,
    ReqQuery = ParsedQs,
    LocalsObj extends Record<string, any> = Record<string, any>,
> {
    // tslint:disable-next-line callable-types (This is extended from and can't extend from a type alias in ts<2.2)
    (
        req: Request<P, ResBody, ReqBody, ReqQuery, LocalsObj>,
        res: Response<ResBody, LocalsObj>,
        next: NextFunction,
    ): void | Promise<void>;    
}

adding the Promise<void> in the types/express@5.0.0 is causing this type issue so that's why it's working in previous versions because the interface returned is only void

[angezy]

The error you're encountering occurs because the tokenVerifier middleware returns a response in case of an error (res.json(...)). The RequestHandler type from Express expects the middleware to either return void or Promise. Since tokenVerifier is returning Response | undefined, TypeScript throws this error.

Here’s how to address it:

Ensure that tokenVerifier always calls next() or returns when it’s done, without returning any response directly.
Update the error handling to avoid returning the Response. Instead, call next with an error to let Express handle it as an error handler.

Here's an updated version of tokenVerifier:

import { NextFunction, Request, Response } from "express";
import { JwtPayload, verify } from "jsonwebtoken";

declare global {
  namespace Express {
    interface Request {
      user?: JwtPayload; // Make user optional to handle cases where it might not be set
    }
  }
}

export const tokenVerifier = (
  req: Request,
  res: Response,
  next: NextFunction
): void => {
  try {
    const authHeader = req.headers.authorization;

    if (!authHeader) {
      return res.status(401).json({
        err: "Authorization token was not provided",
        isSuccess: false,
      });
    }

    const token = authHeader.split(" ")[1];

    req.user = verify(
      token,
      process.env.FLEXIBASE_AUTH_SECRET_KEY!
    ) as JwtPayload;

    next();
  } catch (err) {
    // Pass error to the next middleware
    next(err);
  }
};

Changes Explained

The return type for tokenVerifier is set to void, making sure it either calls next() or returns a response without breaking Express's expected type.
If an error occurs, it calls next(err) instead of returning a Response, allowing Express's error-handling middleware to handle it properly.

If you still encounter issues, make sure that your route handler (verifyUserController) is also typed correctly and doesn’t directly return a response.