Request validation in Node.js - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the Express library.

Node.js

const express = require('[1]');

Drag options to blanks, or click blank then click option'

Afs

Bhttp

Cexpress

Dpath

Attempts:

3 left

💡 Hint

Common Mistakes

Using built-in modules like 'http' instead of 'express'.

The Express library is imported using require('express').

2fill in blank

medium

Complete the code to create a new Express application instance.

Node.js

const app = [1]();

Drag options to blanks, or click blank then click option'

Aexpress

Bhttp

Crouter

Dserver

Attempts:

3 left

💡 Hint

Common Mistakes

Calling a non-existent function like 'http()'.

You create an Express app by calling express().

3fill in blank

hard

Fix the error in the middleware function to correctly parse JSON requests.

Node.js

app.use(express.[1]());

Drag options to blanks, or click blank then click option'

Ajson

Burlencoded

Cstatic

Dtext

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'urlencoded' when expecting JSON data.

To parse JSON request bodies, use express.json() middleware.

4fill in blank

hard

Fill both blanks to validate that the request body has a 'name' property before proceeding.

Node.js

app.post('/submit', (req, res, next) => {
  if (!req.body.[1]) {
    return res.status([2]).send('Name is required');
  }
  next();
});

Drag options to blanks, or click blank then click option'

Aname

B400

C404

Dusername

Attempts:

3 left

💡 Hint

Common Mistakes

Checking for 'username' instead of 'name'.

Using 404 instead of 400 status code.

The code checks if req.body.name exists. If not, it sends a 400 Bad Request status.

5fill in blank

hard

Fill all three blanks to create a middleware that validates 'email' and 'password' fields in the request body.

Node.js

function validateUser(req, res, next) {
  const { [1], [2] } = req.body;
  if (![1] || ![2]) {
    return res.status(400).send('Email and password are required');
  }
  next();
}

Drag options to blanks, or click blank then click option'

Aemail

Bpassword

Cusername

Dtoken

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'username' or 'token' instead of 'email' and 'password'.

The middleware extracts email and password from req.body and checks if both exist before continuing.

Practice

1. What is the main purpose of request validation in a Node.js app?

easy

A. To store data in the database

B. To speed up the server response time

C. To check incoming data before using it

D. To create new routes automatically

Solution

1. Step 1: Understand request validation

   Request validation means checking the data sent by users before the app uses it.

2. Step 2: Identify the main goal

   The goal is to ensure data is safe and correct to avoid errors or security issues.

3. Final Answer:

   To check incoming data before using it -> Option C

4. Quick Check:

   Request validation = check data first [OK]

Hint: Validation means checking data before use [OK]

Common Mistakes:

• Thinking validation speeds up server
• Confusing validation with data storage
• Assuming validation creates routes

2. Which code snippet correctly uses express-validator to check if 'email' is valid?

easy

A. validateEmail('email').isValid()

B. validate('email').isEmail()

C. checkEmail('email').validate()

D. check('email').isEmail()

Solution

1. Step 1: Recall express-validator syntax

   express-validator uses check('fieldName').validationMethod() to validate fields.

2. Step 2: Match correct method for email

   The method is isEmail() to check if the input is a valid email.

3. Final Answer:

   check('email').isEmail() -> Option D

4. Quick Check:

   express-validator uses check() + isEmail() [OK]

Hint: Use check('field').isEmail() for email validation [OK]

Common Mistakes:

• Using validate() instead of check()
• Wrong method names like validateEmail()
• Mixing method order or names

3. Given this code, what will be the output if the request body has { email: 'not-an-email' }?

app.post('/signup', [
  check('email').isEmail(),
  (req, res) => {
    const errors = validationResult(req);
    if (!errors.isEmpty()) {
      return res.status(400).json({ errors: errors.array() });
    }
    res.send('Success');
  }
]);

medium

A. Response with status 400 and error details

B. Response with 'Success' message

C. Server crashes with an error

D. Response with status 200 and empty body

Solution

1. Step 1: Check validation rule

   The rule check('email').isEmail() requires a valid email format.

2. Step 2: Analyze input and error handling

   The input 'not-an-email' fails isEmail(), so errors.isEmpty() is false, triggering status 400 with error details.

3. Final Answer:

   Response with status 400 and error details -> Option A

4. Quick Check:

   Invalid email triggers 400 error [OK]

Hint: Invalid input triggers 400 error with details [OK]

Common Mistakes:

• Assuming success response on invalid input
• Expecting server crash on validation fail
• Ignoring error handling logic

4. Identify the error in this validation middleware:

app.post('/login', [
  check('password').isLength({ min: 6 }),
  (req, res) => {
    const errors = validationResult;
    if (!errors.isEmpty()) {
      return res.status(422).json({ errors: errors.array() });
    }
    res.send('Logged in');
  }
]);

medium

A. validationResult is not called with req, so errors is not an object with isEmpty()

B. isLength should be isMinLength for password check

C. Missing next() call to continue middleware chain

D. Response status 422 is invalid for validation errors

Solution

1. Step 1: Check usage of validationResult

   validationResult must be called as validationResult(req) to get errors from the request.

2. Step 2: Identify the mistake in code

   The code assigns errors = validationResult without calling it, so errors is not an object with isEmpty().

3. Final Answer:

   validationResult is not called with req, so errors is not an object with isEmpty() -> Option A

4. Quick Check:

   Call validationResult(req) to get errors [OK]

Hint: Always call validationResult(req) to get errors [OK]

Common Mistakes:

• Forgetting to call validationResult as a function
• Using wrong validation method names
• Confusing middleware flow with next()

5. You want to validate a request body with fields 'username' (required, min 3 chars) and 'age' (optional, must be a number if present). Which express-validator setup is correct?

hard

A. [check('username').optional().isLength({ min: 3 }), check('age').isNumeric()]

B. [check('username').isLength({ min: 3 }).notEmpty(), check('age').optional().isNumeric()]

C. [check('username').isLength({ min: 3 }), check('age').notEmpty().isNumeric()]

D. [check('username').notEmpty(), check('age').optional().isString()]

Solution

1. Step 1: Validate 'username' requirements

   Username is required and must have at least 3 characters, so use notEmpty() and isLength({ min: 3 }).

2. Step 2: Validate 'age' requirements

   Age is optional but if present must be numeric, so use optional() and isNumeric().

3. Final Answer:

   [check('username').isLength({ min: 3 }).notEmpty(), check('age').optional().isNumeric()] -> Option B

4. Quick Check:

   Required username + optional numeric age = [check('username').isLength({ min: 3 }).notEmpty(), check('age').optional().isNumeric()] [OK]

Hint: Use optional() for optional fields, notEmpty() for required [OK]

Common Mistakes:

• Marking required fields as optional
• Not chaining optional() before other checks
• Using wrong validators like isString() for numbers