express-validator setup - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the output of this express-validator middleware?

Consider this Express route using express-validator. What will be the response if the request body is { "email": "invalidemail", "age": 17 }?

Express

import express from 'express';
import { body, validationResult } from 'express-validator';

const app = express();
app.use(express.json());

app.post('/register', [
  body('email').isEmail(),
  body('age').isInt({ min: 18 })
], (req, res) => {
  const errors = validationResult(req);
  if (!errors.isEmpty()) {
    return res.status(400).json({ errors: errors.array() });
  }
  res.json({ message: 'User registered' });
});

A Status 200 with message 'User registered'

B Status 400 with errors array containing email and age validation errors

C Status 400 with errors array containing only email validation error

D Status 400 with errors array containing only age validation error

💡 Hint

Check which validations fail for the given input values.

The email is invalid and age is less than 18, so both validations fail. The response returns status 400 with both errors.

📝 Syntax

intermediate

Which option correctly imports and uses express-validator in an Express app?

Select the option that correctly sets up express-validator middleware for validating a username field as non-empty.

A

import { body } from 'express-validator';
app.post('/user', [body('username').notEmpty()], handler);

B

const { validate } = require('express-validator');
app.post('/user', [validate('username').notEmpty()], handler);

C

import validator from 'express-validator';
app.post('/user', [validator('username').notEmpty()], handler);

D

import { check } from 'express-validator';
app.post('/user', [check('username').notEmpty()], handler);

💡 Hint

Check the official express-validator import and method names.

Option A correctly imports 'body' from express-validator and uses it to validate the 'username' field.

🔧 Debug

advanced

Why does this express-validator code not catch validation errors?

Given this code snippet, why does the server always respond with 'User created' even if the input is invalid? app.post('/create', [body('email').isEmail()], (req, res) => { res.send('User created'); });

A Because body() middleware is not imported correctly

B Because isEmail() does not validate email format

C Because express.json() middleware is missing

D Because validationResult is not called to check for errors before sending response

💡 Hint

Think about how express-validator reports validation errors.

express-validator requires calling validationResult(req) to check for errors. Without this, errors are ignored.

❓ state_output

advanced

What is the value of errors after this validation?

Given this code snippet, what will be the value of errors.array() if the request body is { "password": "123" }? app.post('/signup', [ body('password').isLength({ min: 6 }) ], (req, res) => { const errors = validationResult(req); res.json({ errors: errors.array() }); });

A [{ msg: 'Password must be at least 6 characters', param: 'password', location: 'body' }]

B []

C [{ msg: 'Invalid value', param: 'password', location: 'body' }]

D null

💡 Hint

Check the default error message for isLength validator.

The default error message for isLength is 'Invalid value' when the length condition fails.

🧠 Conceptual

expert

Which statement about express-validator setup is true?

Choose the correct statement about how express-validator integrates with Express routes.

A validationResult(req) must be called inside the route handler to check for validation errors

B express-validator middleware must be placed before express.json() to parse request body

C express-validator automatically sends error responses if validation fails

D Validation chains can only be used globally, not per route

💡 Hint

Think about how validation errors are handled in express-validator.

express-validator requires explicit call to validationResult(req) inside route handler to check errors. It does not send responses automatically.