app.use(validator()) is not a function

var router = express.Router();
const { check, validationResult } = require('express-validator');

router.post('/register',
  [
    check('email', 'Email is not valid').isEmail(),
    check('username', 'Username field is required').not().isEmpty(),
    check('password', 'Password field is required').not().isEmpty())
  ], 
  function(req, res, next) {

  // Check Errors
  const errors = validationResult(req);
  if (errors) {
    console.log(errors);
    res.render('register', { errors: errors.array() });
  }
  else {
    console.log('No Errors');
    res.render('dashboard', { message: 'Successful Registration.' });
  }
});
// working express validator
// use a different method to Handle errorsconsole.log(`error: ${err}`);
res.status(code).json({
    error: err
});
// good error handling by express validation Pg 2
// make utils/app.js and write this code inside itroute.post([check('nome', 'O nome é obrigatório').not().isEmpty(),
            check('email', 'O email é obrigatório').isEmail(),
            check('password', 'O password é obrigatório').not().isEmpty(),], 

(req, res)=>{

    const errors = validationResult(req);

    if(!errors.isEmpty()){

        app.utils.error.send(errors, req, res);
        return false;
    }

    db.insert(req.body, (err, user)=>{ //entering data into database

        if(err){
            app.utils.error.send(err, req, res);
        }else{
            res.status(200).json(user);
            
        }
    });
// Good Error Handling in express validator Pg 1