Login with MERN Stack, JWT

.env

//.env
JWT_SECRET={{mysecret}}

error.js

class ErrorHandler extends Error {
  constructor(statusCode, message) {
    super();
    this.statusCode = statusCode;
    this.message = message;
  }
}
const handleError = (err, res) => {
  const { statusCode, message } = err;
  res.status(statusCode).json({
    status: "error",
    statusCode,
    message
  });
};
module.exports = {
  ErrorHandler,
  handleError
};

package.json

{
  "name": "backend",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1",
    "start":"node server.js"
  },
  "keywords": [],
  "author": "",
  "license": "ISC",
  "dependencies": {
    "bcryptjs": "^2.4.3",
    "cors": "^2.8.5",
    "dotenv": "^8.2.0",
    "express": "^4.17.1",
    "jsonwebtoken": "^8.5.1",
    "mongoose": "^5.9.5",
    "morgan": "^1.10.0"
  }
}

route.js

const express = require("express");
const router = express.Router();

const userController = require("../controllers/userController");//import userController

router.post("/signup", userController.signup);//get signup function from userController

router.post("/login", userController.login);//get login function from userController

module.exports = router;

server.js

//express
const express = require("express");
const app = express();
const path = require("path");
require("dotenv").config({
  path: path.join(__dirname, "./.env")
});
const PORT = process.env.PORT || 3000;
const routes = require("./routes/route");//imports routes
//imports
const morgan = require("morgan");
var cors = require('cors');
const { handleError, ErrorHandler } = require('./helpers/error')

//mongodb
const mongoose = require("mongoose");

mongoose
  .connect("mongodb://localhost:27017/mernbackend", { useNewUrlParser: true, useUnifiedTopology: true,autoIndex: true ,  useCreateIndex: true,})
  .then(() => {
    console.log("Connected to the Database successfully");
  });
//middlewares
app.use(express.json());
app.use(morgan("dev"));//this will log all the http request in console
app.use(cors()); //for dealing with cross orgin policy
app.use("/", routes); //importing routes from route file
app.use((err, req, res, next) => {
  handleError(err, res);
});//handle error


//server
app.listen(PORT, function() {
  console.log("Server is listening on Port:", PORT);
});

userController.js

const User = require("../models/userModel");
const jwt = require("jsonwebtoken");
const bcrypt = require("bcryptjs");
const { ErrorHandler } = require('../helpers/error');

async function hashPassword(password) {
  return await bcrypt.hash(password, 10);
}
async function validatePassword(plainPassword, hashedPassword) {
  return await bcrypt.compare(plainPassword, hashedPassword);
}
//sign up
exports.signup = async (req, res, next) => {
  try {
    const { email, password } = req.body;
    if (!email || !password) {
      throw new ErrorHandler(404, 'Missing required email and password fields');
    }
      // checking if the email provided already exist in the DB
      const email_exist=await User.findOne({email});
      
          //if it exist we are returning an error message
          if (email_exist) {
               throw new ErrorHandler(409, 'Email already exist!');
          }
    const hashedPassword = await hashPassword(password);
    const newUser = new User({
      email,
      password: hashedPassword,
    
    });
    const accessToken = jwt.sign(
      { userId: newUser._id },
      process.env.JWT_SECRET,
      {
        expiresIn: "1d"
      }
    );
    newUser.accessToken = accessToken;
   await newUser.save();
    res.json({ data: newUser,accessToken });
  } catch (error) {
    next(error);
  }
};

//login
exports.login = async (req, res, next) => {
  try {
    const { email, password } = req.body;
    const user = await User.findOne({ email });
    if (!user) {
      throw new ErrorHandler(401, 'Email does not exist!')
    }
    const validPassword = await validatePassword(password, user.password);
    if (!validPassword) {
      throw new ErrorHandler(404, 'Password is not correct!')
    }
    const accessToken = jwt.sign({ userId: user._id }, process.env.JWT_SECRET, {
      expiresIn: "1d"
    });
    await User.findByIdAndUpdate(user._id, { accessToken });
    res
      .status(200)
      .json({ data: { email: user.email }, accessToken });
  } catch (error) {
    next(error);
  }
};

userModel.js

const mongoose = require("mongoose");
const Schema = mongoose.Schema;
const UserSchema = new Schema({
  email: {
    type: String,
    required: true,
    trim: true,
    unique: true
  },
  password: { type: String, required: true },
  
  
  
});
const User = mongoose.model("user", UserSchema);
module.exports = User;