(node:13612) UnhandledPromiseRejectionWarning: ReferenceError: user is not defined - node.js

Question

I'm trying to login using the id from mongoDB but nodejs keeps giving me this error about user...
(node:13612) UnhandledPromiseRejectionWarning: ReferenceError: user is not defined
registering the user is alright but when calling the login ..... it crashs although everything is defined and I can't figure out why its not reading user from the database
...
const express = require("express");
const { findOne } = require("../models/User");
const router = express.Router();
const User = require("../models/User");
const bcrypt = require("bcryptjs");
const { registerValidation, loginValidation } = require("../validation");
const jwt = require("jsonwebtoken");
router.post("/register", async (req, res) => {
//VALIDATE DATA
const { error } = registerValidation(req.body);
if (error) return res.status(400).send(error.details[0].message);
//CHECK IF USER EXISTS
const emailExist = await User.findOne({ email: req.body.email });
if (emailExist) return res.status(400).send("Email already exists!");
//HASH THE PASSWORD
const salt = await bcrypt.genSalt(10);
const hashPassword = await bcrypt.hash(req.body.password, salt);
//CREATE NEW USER
const user = new User({
name: req.body.name,
email: req.body.email,
password: hashPassword,
});
try {
const savedUser = await user.save();
res.send({user:user._id});
} catch (error) {
res.status(400).send(error);
}
});
router.post("/login", async (req, res) => {
//VALIDATE DATA
const { error } = loginValidation(req.body);
if (error) return res.status(400).send(error.details[0].message);
//CHECK IF USER EXISTS
const emailExist = await User.findOne({ email: req.body.email });
if (!emailExist) return res.status(400).send("Email or Password is Wrong");
//CREATE AND ASSIGN TOKEN
const token = jwt.sign({ _id: user._id }, process.env.TOKEN_SECRET);
res.header("auth-token", token).send(token);
});
module.exports = router;

Answer 1

The issue is an undefined variable:
const token = jwt.sign({ _id: user._id }, process.env.TOKEN_SECRET);
The user (user._id) variable in the line above isn't defined in the Login route, perhaps you meant to find the user first, then to assign the JWT Token?