Validating body fields in Express - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the Express library.

Express

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

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

Aexpress

Bbody-parser

Chttp

Dfs

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'body-parser' instead of 'express'.

Using 'http' which is a Node.js core module.

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

2fill in blank

medium

Complete the code to parse JSON body data in Express.

Express

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

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

Aurlencoded

Bjson

Ctext

Draw

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'urlencoded' when expecting JSON data.

Forgetting to add the middleware.

To parse JSON body data, use express.json() middleware.

3fill in blank

hard

Fix the error in the route handler to access the 'username' field from the request body.

Express

app.post('/login', (req, res) => {
  const username = req.body[1];
  res.send(`Hello, ${username}`);
});

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

A.params.username

B.query.username

C['username']

D.username

Attempts:

3 left

💡 Hint

Common Mistakes

Using req.params or req.query instead of req.body.

Missing quotes in bracket notation.

To access the 'username' field from the body, use req.body['username'] or req.body.username. Here, the blank expects bracket notation.

4fill in blank

hard

Fill both blanks to validate that the 'email' field exists and is a string.

Express

if (typeof req.body[1] === '[2]') {
  res.send('Valid email');
} else {
  res.status(400).send('Invalid email');
}

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

A['email']

Bemail

Cstring

Dnumber

Attempts:

3 left

💡 Hint

Common Mistakes

Using dot notation without quotes in the first blank.

Checking for 'number' instead of 'string'.

Use req.body['email'] to access the email field and check if its type is 'string'.

5fill in blank

hard

Fill all three blanks to create a middleware that checks if 'password' exists and is at least 6 characters long.

Express

function validatePassword(req, res, next) {
  const pwd = req.body[1];
  if (typeof pwd === '[2]' && pwd.length [3] 6) {
    next();
  } else {
    res.status(400).send('Password too short');
  }
}

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

A['password']

Bpassword

C>=

Dstring

Attempts:

3 left

💡 Hint

Common Mistakes

Using dot notation without quotes for password.

Checking length with '<' instead of '>='.

Checking type as 'number' instead of 'string'.

Access the password with req.body['password'], check if it is a 'string', and verify length is at least 6 using >=.

Practice

1. What is the main reason to validate fields in req.body in an Express app?

easy

A. To log user data for analytics

B. To speed up the server response time

C. To change the data format automatically

D. To ensure the data received is complete and correct before processing

Solution

1. Step 1: Understand the purpose of validation

   Validation checks if the data sent by the user is complete and correct.

2. Step 2: Identify the benefit of validation

   It prevents errors and security issues by stopping bad data early.

3. Final Answer:

   To ensure the data received is complete and correct before processing -> Option D

4. Quick Check:

   Validation = Check data correctness [OK]

Hint: Validation means checking data before use [OK]

Common Mistakes:

• Thinking validation speeds up server
• Assuming validation changes data format
• Confusing validation with logging

2. Which middleware is required to parse JSON body data in Express before validating fields?

easy

A. express.json()

B. express.static()

C. express.urlencoded()

D. express.raw()

Solution

1. Step 1: Identify middleware for JSON parsing

   express.json() parses incoming JSON request bodies into JavaScript objects.

2. Step 2: Compare with other middleware

   express.urlencoded() parses URL-encoded data, express.static() serves files, express.raw() parses raw buffer data.

3. Final Answer:

   express.json() -> Option A

4. Quick Check:

   JSON body parsing = express.json() [OK]

Hint: Use express.json() to parse JSON body data [OK]

Common Mistakes:

• Using express.static() for body parsing
• Confusing urlencoded with JSON parsing
• Skipping middleware before validation

3. Given this Express route, what will be the response if req.body.name is missing?

app.post('/user', (req, res) => {
  if (!req.body.name) {
    return res.status(400).send('Name is required');
  }
  res.send(`Hello, ${req.body.name}`);
});

medium

A. Hello, undefined

B. Name is required

C. 500 Internal Server Error

D. Empty response

Solution

1. Step 1: Check the condition for missing name

   The code checks if req.body.name is falsy (missing or empty).

2. Step 2: Understand the response when name is missing

   If missing, it sends status 400 with message 'Name is required'.

3. Final Answer:

   Name is required -> Option B

4. Quick Check:

   Missing name triggers 400 error message [OK]

Hint: Missing field triggers error response [OK]

Common Mistakes:

• Assuming undefined is sent as name
• Expecting server error instead of 400
• Thinking response is empty

4. What is wrong with this Express validation code?

app.post('/login', (req, res) => {
  if (req.body.username === undefined || req.body.password === undefined) {
    res.status(400).send('Missing fields');
  }
  res.send('Login success');
});

medium

A. It should check for null instead of undefined

B. It uses strict equality instead of loose equality

C. It does not stop execution after sending error response

D. It should use res.json() instead of res.send()

Solution

1. Step 1: Analyze the error handling flow

   The code sends a 400 error but does not return or stop, so it continues to send success response.

2. Step 2: Identify the fix

   Adding 'return' before res.status(400).send(...) stops further execution.

3. Final Answer:

   It does not stop execution after sending error response -> Option C

4. Quick Check:

   Missing return causes double response [OK]

Hint: Return after sending error to stop code [OK]

Common Mistakes:

• Ignoring missing return after res.send()
• Confusing equality checks with flow control
• Thinking res.json() is required for errors

5. You want to validate that req.body.age is a number greater than 18 before processing. Which code snippet correctly validates this and sends a 400 error if invalid?

hard

A. if (!req.body.age || typeof req.body.age !== 'number' || req.body.age <= 18) {
return res.status(400).send('Age must be a number over 18');
}

B. if (req.body.age <= 18) {
res.status(400).send('Age must be over 18');
}

C. if (typeof req.body.age === 'string' && req.body.age > 18) {
return res.status(400).send('Invalid age');
}

D. if (!req.body.age || req.body.age < 18) {
res.send('Age is valid');
}

Solution

1. Step 1: Check for presence and type of age

   Code verifies age exists and is a number using typeof.

2. Step 2: Check age value is greater than 18

   It ensures age is over 18, else sends 400 error with message.

3. Step 3: Confirm proper use of return to stop execution

   Return stops further processing after error response.

4. Final Answer:

   if (!req.body.age || typeof req.body.age !== 'number' || req.body.age <= 18) { return res.status(400).send('Age must be a number over 18'); } -> Option A

5. Quick Check:

   Check presence, type, and value with return [OK]

Hint: Check type and value, return on error [OK]

Common Mistakes:

• Not checking type before comparing
• Missing return after sending error
• Sending success message on invalid data