error.js

const ErrorHandler = require("../utils/errorhandler");

module.exports = (err, req, res, next) => {
  err.statusCode = err.statusCode || 500;
  err.message = err.message || "Internal Server Error";

  //Wrong Mongodb ID Error
  if (err.name === "CastError") {
    const message = `Resource not found. Invalid ${err.path}`; //err.path -> line at which error has occured
    err = new ErrorHandler(message, 400);
  }

  //Mongoose Duplicate key error
  if (err.code === 11000) {
    const message = `Duplicate ${Object.keys(err.keyValue)} Entered`; // 'Object.keys(err.keyValue)' is use to retrieve whatever the error is.
    err = new ErrorHandler(message, 400);
  }

  //Wrong JWT error
  if (err.name === "JsonWebTokenError") {
    const message = `Json Web Token is invalid, Try again`;
    err = new ErrorHandler(message, 400);
  }

  //JWT Expire Error
  if (err.name === "TokenExpiredError") {
    const message = `Json Web Token is Expired, Try again`;
    err = new ErrorHandler(message, 400);
  }

  res.status(err.statusCode).json({
    success: false,
    message: err.message,
  });
};