Request and response schemas 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'

Afs

Bhttp

Cpath

Dexpress

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'http' instead of 'express' for the import.

Forgetting to put quotes around the package name.

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

2fill in blank

medium

Complete the code to define a POST route that expects JSON data.

Express

app.post('/data', (req, res) => {
  const userData = req.[1];
  res.send('Received');
});

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

Aquery

Bparams

Cbody

Dheaders

Attempts:

3 left

💡 Hint

Common Mistakes

Using req.params or req.query to get JSON data.

Not using middleware to parse JSON before accessing req.body.

The JSON data sent in a POST request is accessed via req.body.

3fill in blank

hard

Fix the error in the response to send JSON data correctly.

Express

res.[1]({ message: 'Success' });

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

Ajson

Bend

Cwrite

Dsend

Attempts:

3 left

💡 Hint

Common Mistakes

Using res.send() without setting headers explicitly.

Using res.write() or res.end() which are lower-level methods.

Use res.json() to send a JSON response with the correct headers.

4fill in blank

hard

Fill both blanks to validate request data and send an error response if invalid.

Express

if (!req.body.name || typeof req.body.name !== '[1]') {
  return res.status([2]).json({ error: 'Name is required and must be a string' });
}

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

Astring

Bnumber

C400

D404

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong data type in typeof check.

Using 404 status code which means not found.

The code checks if name is a string and sends a 400 Bad Request status if not.

5fill in blank

hard

Fill all three blanks to create a response schema that sends user info with id, name, and active status.

Express

res.json({
  id: req.body.[1],
  name: req.body.[2],
  active: req.body.[3]
});

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

AuserId

Bname

Cactive

Demail

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong property names that don't exist in req.body.

Including unrelated fields like email when not required.

The response sends userId, name, and active fields from the request body.

Practice

1. What is the main purpose of using request and response schemas in an Express app?

easy

A. To define and validate the shape of data sent and received

B. To speed up the server response time

C. To style the API responses with colors

D. To automatically generate HTML pages

Solution

1. Step 1: Understand the role of schemas

   Request and response schemas specify what data structure is expected, helping to validate inputs and outputs.

2. Step 2: Identify the main benefit

   This validation helps catch errors early and keeps the API clear and consistent.

3. Final Answer:

   To define and validate the shape of data sent and received -> Option A

4. Quick Check:

   Schema purpose = validation [OK]

Hint: Schemas check data shape to avoid errors [OK]

Common Mistakes:

• Thinking schemas improve speed directly
• Confusing schemas with styling tools
• Assuming schemas generate HTML automatically

2. Which of the following is the correct way to use a schema validation middleware in Express for a POST request body?

easy

A. app.get('/user', validateSchema, (req, res) => { ... })

B. app.post('/user', validateSchema, (req, res) => { ... })

C. app.post('/user', (req, res) => validateSchema(req.body))

D. app.use(validateSchema('/user'))

Solution

1. Step 1: Identify correct HTTP method and middleware usage

   Schema validation middleware should be used in the route handler chain, typically for POST requests when validating request bodies.

2. Step 2: Check syntax correctness

   app.post('/user', validateSchema, (req, res) => { ... }) correctly places the middleware function before the route handler for POST '/user'.

3. Final Answer:

   app.post('/user', validateSchema, (req, res) => { ... }) -> Option B

4. Quick Check:

   Middleware before handler for POST = B [OK]

Hint: Middleware goes between route and handler [OK]

Common Mistakes:

• Using GET instead of POST for body validation
• Calling middleware inside handler instead of chaining
• Using app.use incorrectly with route path

3. Given this Express route using Joi schema validation middleware:

const schema = Joi.object({ name: Joi.string().required() });
app.post('/data', (req, res, next) => {
  const { error } = schema.validate(req.body);
  if (error) return res.status(400).send(error.message);
  res.send('Valid data');
});

What will the response be if the client sends {} as JSON body?

medium

A. Valid data

B. 500 Internal Server Error

C. 400 Bad Request with error message

D. Empty response with status 200

Solution

1. Step 1: Analyze schema requirements

   The schema requires a 'name' string field that is mandatory.

2. Step 2: Check validation result for empty body

   Sending an empty object {} misses the required 'name', so validation fails and error is returned with status 400.

3. Final Answer:

   400 Bad Request with error message -> Option C

4. Quick Check:

   Missing required field = 400 error [OK]

Hint: Missing required fields cause 400 error [OK]

Common Mistakes:

• Assuming empty body passes validation
• Expecting 500 error on validation failure
• Thinking success message is sent regardless

4. Consider this Express route snippet with schema validation:

app.post('/item', (req, res) => {
  const { id, price } = req.body;
  if (typeof id !== 'number' || typeof price !== 'number') {
    res.status(400).send('Invalid data');
    return;
  }
  res.send('Item accepted');
});

What is the main bug in this code?

medium

A. It does not stop execution after sending 400 response

B. It uses wrong HTTP method for data submission

C. It does not parse JSON body before accessing req.body

D. It sends response twice causing server crash

Solution

1. Step 1: Check response flow after validation failure

   After sending 400 response, the code continues and sends 'Item accepted' response, causing multiple responses.

2. Step 2: Identify missing control flow

   There is no return or else to stop execution after sending error response.

3. Final Answer:

   It does not stop execution after sending 400 response -> Option A

4. Quick Check:

   Send response then stop = return [OK]

Hint: Return after res.send to stop code [OK]

Common Mistakes:

• Ignoring missing return after error response
• Assuming Express auto-stops after res.send
• Confusing HTTP method correctness

5. You want to create an Express route that accepts a JSON body with an array of user objects, each having a required 'email' string and optional 'age' number. Which Joi schema correctly validates this request body?

hard

A. Joi.object({ users: Joi.array().required() })

B. Joi.object({ email: Joi.string().required(), age: Joi.number() }).required()

C. Joi.array().items(Joi.string().email().required())

D. Joi.array().items(Joi.object({ email: Joi.string().email().required(), age: Joi.number() }))

Solution

1. Step 1: Understand the data shape

   The body is an array of user objects, each with required 'email' string and optional 'age' number.

2. Step 2: Match schema to data shape

   Joi.array().items(Joi.object({ email: Joi.string().email().required(), age: Joi.number() })) defines an array of objects with the correct fields and validations.

3. Final Answer:

   Joi.array().items(Joi.object({ email: Joi.string().email().required(), age: Joi.number() })) -> Option D

4. Quick Check:

   Array of objects with required email = A [OK]

Hint: Use array().items(object({...})) for arrays of objects [OK]

Common Mistakes:

• Using object schema instead of array for array data
• Validating array of strings instead of objects
• Missing required email validation