Schema validation in Express - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the schema validation library.

Express

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

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

Abody-parser

Bexpress

Cmongoose

Djoi

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'express' instead of 'joi'.

Trying to import 'mongoose' which is for databases.

We use joi to define and validate schemas in Express apps.

2fill in blank

medium

Complete the code to define a schema for a user with a required string name.

Express

const schema = Joi.object({ name: Joi.[1]().required() });

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

Astring

Bnumber

Cboolean

Darray

Attempts:

3 left

💡 Hint

Common Mistakes

Using number() for a name.

Using array() which is for lists.

The string() method defines a string type in Joi schemas.

3fill in blank

hard

Fix the error in the validation call to check the request body.

Express

const { error } = schema.[1](req.body);

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

Avalidate

Btest

Ccheck

DvalidateBody

Attempts:

3 left

💡 Hint

Common Mistakes

Using non-existent methods like validateBody or check.

Confusing with test which is not a Joi method.

The correct method to validate data with Joi is validate().

4fill in blank

hard

Fill both blanks to create middleware that validates the request body and sends an error if invalid.

Express

function validateUser(req, res, next) {
  const { error } = schema.[1](req.body);
  if (error) return res.status([2]).send(error.details[0].message);
  next();
}

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

Avalidate

B400

C500

Dcheck

Attempts:

3 left

💡 Hint

Common Mistakes

Using status 500 which means server error, not client error.

Using a wrong method like 'check' instead of 'validate'.

Use validate to check the data and send status 400 for bad requests.

5fill in blank

hard

Fill all three blanks to define a schema with a required string 'username', an optional number 'age', and validate an object.

Express

const schema = Joi.object({
  username: Joi.[1]().required(),
  age: Joi.[2](),
});

const { error } = schema.[3]({ username: 'Alice', age: 30 });

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

Astring

Bnumber

Cvalidate

Dboolean

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up data types like using boolean for age.

Forgetting to call 'validate' to check the data.

Use string() for username, number() for age, and validate() to check the object.

Practice

1. What is the main purpose of schema validation in an Express app?

easy

A. To store data permanently in the database

B. To speed up the server response time

C. To style the user interface automatically

D. To check if incoming data matches expected rules before processing

Solution

1. Step 1: Understand schema validation role

   Schema validation ensures data received matches rules like type and format.

2. Step 2: Identify main purpose in Express

   It prevents bad data from causing errors or security issues by checking before use.

3. Final Answer:

   To check if incoming data matches expected rules before processing -> Option D

4. Quick Check:

   Schema validation = data check before use [OK]

Hint: Schema validation means checking data fits rules before use [OK]

Common Mistakes:

• Thinking validation speeds up server
• Confusing validation with UI styling
• Assuming validation stores data

2. Which of the following is the correct way to define a Joi schema for a required string named username?

easy

A. const schema = Joi.object({ username: Joi.string().required() });

B. const schema = Joi.string().required();

C. const schema = Joi.string().optional();

D. const schema = Joi.number().required();

Solution

1. Step 1: Recall Joi schema structure for objects

   Joi schemas for objects use Joi.object({ key: rule }) format.

2. Step 2: Check correct rule for required string property

   Property username must be a string and required, so use Joi.string().required().

3. Final Answer:

   const schema = Joi.object({ username: Joi.string().required() }); -> Option A

4. Quick Check:

   Object schema with required string property = const schema = Joi.object({ username: Joi.string().required() }); [OK]

Hint: Use Joi.object({ key: Joi.type().required() }) for required fields [OK]

Common Mistakes:

• Defining schema as Joi.string() alone for object data
• Using optional() instead of required()
• Using wrong data type like Joi.number() for string

3. Given this Joi schema and data, what will schema.validate(data) return?

const schema = Joi.object({ age: Joi.number().min(18).required() });
const data = { age: 16 };

medium

A. Validation fails because age is less than 18

B. Validation passes with value { age: 16 }

C. Validation fails because age is missing

D. Validation passes with value { age: 18 }

Solution

1. Step 1: Analyze schema rules for age

   Age must be a number, minimum 18, and required.

2. Step 2: Check data against schema

   Data has age 16, which is less than minimum 18, so validation fails.

3. Final Answer:

   Validation fails because age is less than 18 -> Option A

4. Quick Check:

   Age < 18 fails min rule = Validation fails because age is less than 18 [OK]

Hint: Check min/max rules carefully when validating numbers [OK]

Common Mistakes:

• Assuming 16 passes min(18) rule
• Confusing missing field with invalid value
• Thinking Joi changes value automatically

4. What is wrong with this Express route using Joi validation?

app.post('/user', (req, res) => {
  const schema = Joi.object({ email: Joi.string().email().required() });
  const result = schema.validate(req.body.email);
  if (result.error) {
    res.status(400).send('Invalid email');
  } else {
    res.send('User created');
  }
});

medium

A. It does not call next() after validation

B. It validates only the email string, not the whole object

C. It uses res.send instead of res.json

D. It should use Joi.number() for email

Solution

1. Step 1: Check what is validated

   The schema expects an object with an email property, but code validates req.body.email (a string).

2. Step 2: Understand Joi object validation

   To validate the whole object, pass req.body to schema.validate, not just one property.

3. Final Answer:

   It validates only the email string, not the whole object -> Option B

4. Quick Check:

   Validate whole object, not single property [OK]

Hint: Validate req.body object, not a single field string [OK]

Common Mistakes:

• Validating only a property instead of full object
• Confusing res.send and res.json (both work)
• Forgetting to call next() is not required here
• Using wrong Joi type for email

5. You want to validate a user object with optional phone that must be a string of 10 digits if present, and a required name string. Which Joi schema correctly enforces this?

hard

A. Joi.object({ name: Joi.string().required(), phone: Joi.string().pattern(/\d+/).required() })

B. Joi.object({ name: Joi.string(), phone: Joi.number().length(10).optional() })

C. Joi.object({ name: Joi.string().required(), phone: Joi.string().pattern(/^\d{10}$/).optional() })

D. Joi.object({ name: Joi.string().required(), phone: Joi.string().length(10).required() })

Solution

1. Step 1: Identify required and optional fields

   Name is required string; phone is optional string matching exactly 10 digits.

2. Step 2: Check regex pattern and optional usage

   Pattern /^\d{10}$/ matches exactly 10 digits; phone is optional, so use .optional().

3. Step 3: Eliminate incorrect options

   Other options make phone required, use wrong types like Joi.number(), apply invalid methods like .length(10) on numbers, or use loose patterns like /\d+/.

4. Final Answer:

   Joi.object({ name: Joi.string().required(), phone: Joi.string().pattern(/^\d{10}$/).optional() }) -> Option C

5. Quick Check:

   Required name + optional 10-digit phone pattern = Joi.object({ name: Joi.string().required(), phone: Joi.string().pattern(/^\d{10}$/).optional() }) [OK]

Hint: Use .pattern(/^\d{10}$/) for exact 10-digit string [OK]

Common Mistakes:

• Using Joi.number() for phone instead of string
• Making optional field required
• Using .length(10) on string without pattern
• Using loose regex that allows wrong formats