TypeError: req.checkBody is not a function

With express-validator 6 you will have to do the following:

import

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

validation

body('username').isEmail()
body('password').isLength({ min: 5 })

errors

const errors = validationResult(req);

You need to install express-validator using below command

npm install express-validator

then add

var expressValidator = require('express-validator');
api.use(expressValidator())

immediately after

var api = express.Router();

See TypeError: req.checkBody is not a function including bodyparser and expressvalidator module for more details