I’m having trouble with a custom error class in TypeScript where the modified error message does not display correctly, I just get the error message returned from the API call.
My customError classs–

export class CustomError extends Error {
    cod:string;
    constructor(cod:string , message: string){
        super(message);
        this.cod = cod;
        Object.setPrototypeOf(this , new.target.prototype);

        if (Error.captureStackTrace) {
            Error.captureStackTrace(this, this.constructor);
        }
    }
}

The class inheriting–

import { CustomError } from "./CustomError";

export class CityNotFoundError extends CustomError {
    constructor(cod:string , message: string){
        const errMsg:string = message + " :The city you provided was not found,Please verify"
        super(cod,errMsg);
    }
}

The error handler function.

import { CityNotFoundError } from "../Errors/CityNotFoundError";
export function ErrorHandler(cod: string , message: string){
    switch(cod){
        case '404':
            const errMsg:string = message + " :The city you provided was not found,Please verify"
            return new CityNotFoundError(cod,errMsg);
    }
}

This is the function

app.get('/',async (req:Request,res:Response) =>{
    await fetch(`https://api.openweathermap.org/data/2.5/weather?q={location}&&appid={API_KEY}`).
    then(async(response) =>{ 
        const data = await response.json();
        console.log(data)
        res.json(data);
    }).
        catch(async(err) =>{
            const error = ErrorHandler(err.cod , err.message)!;
            console.error(error.stack);
            res.status(500).json({
                code: error.cod,
                message: error.message,
            });
        })
})

I get this error { cod: ‘404’, message: ‘city not found’ }
but I want this..
{ cod: ‘404’, message: ‘city not found: :The city you provided was not found,Please verify’ }

What might be causing the issue where the error message is not modified as expected? How can I ensure that the additional context I add in the CityNotFoundError constructor is included in the error message when it is logged?