Input validation and sanitization in Node.js - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the Express framework.

Node.js

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

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

Aexpress

Bhttp

Cfs

Dpath

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'http' instead of 'express' to import the framework.

The Express framework is imported by requiring 'express'.

2fill in blank

medium

Complete the code to use the express.json() middleware for parsing JSON input.

Node.js

app.use([1]());

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

AcookieParser

Bexpress.json

CbodyParser.text

Dexpress.urlencoded

Attempts:

3 left

💡 Hint

Common Mistakes

Using express.urlencoded() which parses URL-encoded data instead of JSON.

express.json() middleware parses incoming JSON requests.

3fill in blank

hard

Fix the error in the validation code to check if the input 'age' is a number.

Node.js

if (typeof [1] !== 'number') {
  res.status(400).send('Age must be a number');
}

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

Areq.body.age

Breq.params.age

Creq.query.age

Dreq.age

Attempts:

3 left

💡 Hint

Common Mistakes

Using req.params.age or req.query.age when input is sent in JSON body.

Input data from JSON body is accessed via req.body.age.

4fill in blank

hard

Fill both blanks to sanitize and validate a username input using the 'validator' library.

Node.js

const sanitizedUsername = validator.[1](req.body.username);
if (!validator.[2](sanitizedUsername)) {
  res.status(400).send('Invalid username');
}

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

Aescape

BisEmail

CisAlphanumeric

Dtrim

Attempts:

3 left

💡 Hint

Common Mistakes

Using isEmail() to validate username which is incorrect.

Use escape() to sanitize input and isAlphanumeric() to validate username characters.

5fill in blank

hard

Fill all three blanks to create a middleware that validates and sanitizes an email input.

Node.js

function validateEmail(req, res, next) {
  const email = validator.[1](req.body.email);
  if (!validator.[2](email)) {
    return res.status(400).send('Invalid email');
  }
  req.body.email = email[3]();
  next();
}

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

AnormalizeEmail

BisEmail

Ctrim

Descape

Attempts:

3 left

💡 Hint

Common Mistakes

Using escape() on email which can break the format.

normalizeEmail() cleans the email, isEmail() validates it, and trim() removes extra spaces.

Practice

1. What is the main purpose of input validation in a Node.js application?

easy

A. To check if the input data is correct and safe before processing

B. To store user data in the database

C. To format the output data for display

D. To speed up the server response time

Solution

1. Step 1: Understand input validation

   Input validation ensures that the data received from users meets expected rules and is safe to use.

2. Step 2: Identify the purpose in Node.js

   In Node.js, input validation prevents bad or harmful data from causing errors or security issues.

3. Final Answer:

   To check if the input data is correct and safe before processing -> Option A

4. Quick Check:

   Input validation = check data safety [OK]

Hint: Validation means checking data correctness and safety [OK]

Common Mistakes:

• Confusing validation with data storage
• Thinking validation formats output
• Assuming validation improves speed

2. Which of the following is the correct way to import the express-validator middleware in a Node.js file using ES modules?

easy

A. const { check } = require('express-validator');

B. import check from 'express-validator';

C. const check = require('express-validator/check');

D. import { check } from 'express-validator';

Solution

1. Step 1: Identify modern import syntax

   Node.js with ES modules uses import { check } from 'express-validator'; to import named exports.

2. Step 2: Check other options

   const { check } = require('express-validator'); uses CommonJS require but destructuring is possible only if CommonJS is used; import check from 'express-validator'; imports default which express-validator does not export; const check = require('express-validator/check'); uses a wrong path.

3. Final Answer:

   import { check } from 'express-validator'; -> Option D

4. Quick Check:

   Use ES module import for express-validator [OK]

Hint: Use ES module import syntax with curly braces for named exports [OK]

Common Mistakes:

• Using require instead of import in ES modules
• Importing default instead of named export
• Using incorrect module paths

3. Consider this Node.js code snippet using express-validator:

app.post('/submit', [
  check('email').isEmail(),
  check('age').isInt({ min: 18 })
], (req, res) => {
  const errors = validationResult(req);
  if (!errors.isEmpty()) {
    return res.status(400).json({ errors: errors.array() });
  }
  res.send('Data is valid');
});

What will be the response if the user sends { "email": "userexample.com", "age": 17 }?

medium

A. Status 400 with error about missing fields

B. Status 400 with errors about invalid email and age

C. Status 500 server error

D. Status 200 with message 'Data is valid'

Solution

1. Step 1: Analyze validation rules

   The code checks if 'email' is a valid email and 'age' is an integer >= 18.

2. Step 2: Check input values

   The email 'userexample.com' is missing '@', so invalid. Age 17 is less than 18, so invalid.

3. Final Answer:

   Status 400 with errors about invalid email and age -> Option B

4. Quick Check:

   Invalid email and age cause 400 error [OK]

Hint: Invalid inputs trigger 400 with error details [OK]

Common Mistakes:

• Assuming invalid data passes validation
• Confusing status codes
• Ignoring validationResult usage

4. You wrote this code to sanitize input but it doesn't remove spaces as expected:

app.post('/data', [
  check('username').trim().escape()
], (req, res) => {
  // ...
});

What is the likely reason the spaces are not removed?

medium

A. You must call sanitize() before trim()

B. escape() removes spaces but trim() does not

C. The trim() method removes spaces only from start and end, not inside the string

D. The check() function does not support trim()

Solution

1. Step 1: Understand trim() behavior

   The trim() method removes whitespace only from the start and end of a string, not inside it.

2. Step 2: Check escape() effect

   escape() converts special characters but does not remove spaces inside the string.

3. Final Answer:

   The trim() method removes spaces only from start and end, not inside the string -> Option C

4. Quick Check:

   trim() trims edges, not inner spaces [OK]

Hint: trim() only removes spaces at string ends [OK]

Common Mistakes:

• Expecting trim() to remove all spaces
• Misunderstanding escape() purpose
• Thinking check() lacks trim() support

5. You want to create a Node.js API endpoint that accepts a username and email. The username must be alphanumeric and trimmed, and the email must be valid and normalized. Which express-validator chain correctly applies validation and sanitization?

hard

A. [ check('username').trim().isAlphanumeric(), check('email').normalizeEmail().isEmail() ]

B. [ check('username').isAlphanumeric().trim(), check('email').isEmail().normalizeEmail() ]

C. [ check('username').escape().isAlphanumeric(), check('email').isEmail().trim() ]

D. [ check('username').isAlphanumeric().escape(), check('email').trim().normalizeEmail() ]

Solution

1. Step 1: Validate username and email correctly

   Username must be alphanumeric and trimmed, so trim() before or after is okay but isAlphanumeric() must check the trimmed string. Email must be checked with isEmail() and normalized with normalizeEmail().

2. Step 2: Analyze options

   [ check('username').trim().isAlphanumeric(), check('email').normalizeEmail().isEmail() ] applies trim() before isAlphanumeric() which ensures validation on trimmed string; [ check('username').isAlphanumeric().trim(), check('email').isEmail().normalizeEmail() ] applies isAlphanumeric() before trim(), which may validate untrimmed input; also, normalizeEmail() should come before isEmail() to validate normalized email; [ check('username').escape().isAlphanumeric(), check('email').isEmail().trim() ] escapes username unnecessarily and trims email which is not needed; [ check('username').isAlphanumeric().escape(), check('email').trim().normalizeEmail() ] escapes username and trims email incorrectly.

3. Final Answer:

   [ check('username').trim().isAlphanumeric(), check('email').normalizeEmail().isEmail() ] -> Option A

4. Quick Check:

   Trim before validation for username; normalize before validation for email [OK]

Hint: Trim before validation for username; normalize before validation for email [OK]

Common Mistakes:

• Applying sanitization after validation incorrectly
• Using escape() unnecessarily
• Trimming email instead of normalizing