How to resolve TypeScript type error with jwt.sign and Secret in jsonwebtoken?

I'm working on a TypeScript project where I'm using the jsonwebtoken library to generate and verify JWT tokens. However, I'm encountering a type error when trying to use the jwt.sign function.

import jwt, { Secret, JwtPayload } from "jsonwebtoken";

const JWT_SECRET: Secret = process.env.JWT_SECRET || "kala__30191";
const EXPIRE: string = process.env.JWT_EXPIRE || "30d";

export function generateToken(payload: Record<string, any>): string {
  return jwt.sign(payload, JWT_SECRET, { expiresIn: EXPIRE });
}

export function verifyToken(token: string): Promise<JwtPayload | string> {
  return new Promise((resolve, reject) => {
    jwt.verify(token, JWT_SECRET, (err, decoded) => {
      if (err) {
        return reject(err);
      }
      resolve(decoded as JwtPayload);
    });
  });
}

But I am getting the some error, that i cannot understand.

No overload matches this call.
Overload 1 of 5, '(payload: string | object | Buffer<ArrayBufferLike>, secretOrPrivateKey: null, options?: (SignOptions & { algorithm: "none"; }) | undefined): string', gave the following error.
Argument of type 'Secret' is not assignable to parameter of type 'null'.
Type 'string' is not assignable to type 'null'.
Overload 2 of 5, '(payload: string | object | Buffer<ArrayBufferLike>, secretOrPrivateKey: Secret | Buffer<ArrayBufferLike> | PrivateKeyInput | JsonWebKeyInput, options?: SignOptions | undefined): string', gave the following error.
Type 'string' is not assignable to type 'number | StringValue | undefined'.
Overload 3 of 5, '(payload: string | object | Buffer<ArrayBufferLike>, secretOrPrivateKey: Secret | Buffer<ArrayBufferLike> | PrivateKeyInput | JsonWebKeyInput, callback: SignCallback): void', gave the following error.
Object literal may only specify known properties, and 'expiresIn' does not exist in type 'SignCallback'. (ts 2769)

I have installed the jsonwebtoken library and its type definitions. I'm looking for guidance on how to fix this type error.

Solution

jwt.sign expects the expiresIn option to be of type number | StringValue | undefined but you defined EXPIRE to be a string.

I checked the definition of StringValue (here) and it is basically a way to get type safety for constructs like 30d which you used for a value.

Simply not forcing EXPIRE to be a string and letting the type system infer the proper type should be sufficient to fix your problem:

const EXPIRE = process.env.JWT_EXPIRE || "30d";

This might get you a new issue because process.env.JWT_EXPIRE is probably defined as string | undefined as well. In this case you may have to bite the bullet and define it to be any:

const EXPIRE = process.env.JWT_EXPIRE as any || "30d";

Note: You could (should?) also add an additional dependency @types/ms and use the StringValue type that it defines.

import type { StringValue } from "ms";
const EXPIRE = process.env.JWT_EXPIRE as StringValue || "30d";