Pagination patterns in Node.js - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to set the default page number to 1 if not provided.

Node.js

const page = parseInt(req.query.page) || [1];

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

A1

B0

Cnull

Dundefined

Attempts:

3 left

💡 Hint

Common Mistakes

Using 0 as the default page number, which may cause confusion.

Using null or undefined which do not default properly.

The default page number should be 1 to start pagination from the first page.

2fill in blank

medium

Complete the code to calculate the number of items to skip based on page and limit.

Node.js

const skip = (page - 1) * [1];

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

Apage

Bcount

Climit

Doffset

Attempts:

3 left

💡 Hint

Common Mistakes

Using page instead of limit causes wrong skip calculation.

Using offset or count which are not defined here.

We multiply (page - 1) by the limit to skip the correct number of items.

3fill in blank

hard

Fix the error in the MongoDB query to apply pagination correctly.

Node.js

const results = await collection.find().skip([1]).limit(limit).toArray();

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

A(page - 1) * limit

Bskip

Cpage

Doffset

Attempts:

3 left

💡 Hint

Common Mistakes

Passing page directly to skip causes wrong results.

Using undefined variables like offset.

The skip value must be calculated as (page - 1) * limit to get the correct starting point.

4fill in blank

hard

Fill both blanks to create a paginated API response with total pages and current page.

Node.js

const totalPages = Math.ceil(totalItems / [1]);
const response = { currentPage: [2], totalPages };

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

Alimit

Bpage

Cskip

Dcount

Attempts:

3 left

💡 Hint

Common Mistakes

Using skip instead of limit for total pages calculation.

Mixing up page and skip values.

Total pages is total items divided by limit, rounded up. Current page is the page number requested.

5fill in blank

hard

Fill all three blanks to implement cursor-based pagination with limit and cursor parameters.

Node.js

const query = {};
if ([1]) {
  query._id = { $gt: [2] };
}
const results = await collection.find(query).limit([3]).toArray();

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

Acursor

Climit

Dpage

Attempts:

3 left

💡 Hint

Common Mistakes

Using page instead of cursor for _id comparison.

Not limiting the results properly.

If a cursor is provided, query for items with _id greater than cursor. Limit the results by the limit value.

Practice

1.

What is the main purpose of pagination in a Node.js application?

easy

A. To combine all data into one large response

B. To split large data into smaller pages for faster loading and better user experience

C. To delete old data automatically

D. To encrypt data before sending it to the client

Solution

1. Step 1: Understand pagination concept

   Pagination divides data into smaller chunks or pages to avoid loading everything at once.

2. Step 2: Identify the benefit in Node.js apps

   This improves speed and usability by sending only a subset of data per request.

3. Final Answer:

   To split large data into smaller pages for faster loading and better user experience -> Option B

4. Quick Check:

   Pagination = split data for speed [OK]

Hint: Pagination means splitting data into pages for faster loading [OK]

Common Mistakes:

• Thinking pagination deletes data
• Confusing pagination with encryption
• Assuming pagination combines all data

2.

Which of the following is the correct way to use limit and offset for pagination in a SQL query within Node.js?

SELECT * FROM users ORDER BY id ASC LIMIT ? OFFSET ?;

easy

A. limit = number of items per page, offset = (page number - 1) * number of items per page

B. limit = page number, offset = number of items per page

C. limit = total items, offset = 0

D. limit = number of items per page, offset = page number

Solution

1. Step 1: Understand limit and offset roles

   Limit controls how many items to fetch; offset skips items before starting.

2. Step 2: Calculate offset for pagination

   Offset should skip items from previous pages: (page number - 1) * items per page.

3. Final Answer:

   limit = number of items per page, offset = (page number - 1) * number of items per page -> Option A

4. Quick Check:

   Offset skips previous pages = (page-1)*limit [OK]

Hint: Offset skips previous pages: (page-1) times limit [OK]

Common Mistakes:

• Using offset as page number directly
• Swapping limit and offset values
• Setting offset to page number without calculation

3.

Given this Node.js code snippet using a database query for pagination:

const page = 3;
const limit = 10;
const offset = (page - 1) * limit;
const results = await db.query('SELECT * FROM products ORDER BY id ASC LIMIT ? OFFSET ?', [limit, offset]);
console.log(results.length);

If the database has 25 products, what will results.length print?

medium

A. 25

B. 10

C. 15

D. 5

Solution

1. Step 1: Calculate offset and limit values

   Page 3 means offset = (3-1)*10 = 20, limit = 10.

2. Step 2: Determine how many products remain after offset

   There are 25 products total, offset 20 skips first 20, leaving 5 products.

3. Final Answer:

   5 -> Option D

4. Quick Check:

   Remaining items after offset = 5 [OK]

Hint: Last page may have fewer items than limit [OK]

Common Mistakes:

• Assuming full limit items always returned
• Calculating offset incorrectly
• Ignoring total number of products

4.

Identify the error in this Node.js pagination code snippet:

const page = 0;
const limit = 10;
const offset = page * limit;
const results = await db.query('SELECT * FROM items LIMIT ? OFFSET ?', [limit, offset]);

What is the problem with this code?

medium

A. Offset should be negative for first page

B. Limit should be zero to fetch all items

C. Page number should start from 1, not 0, causing incorrect offset

D. Query syntax is invalid with placeholders

Solution

1. Step 1: Check page number usage

   Page is set to 0, but pagination usually starts at 1.

2. Step 2: Calculate offset impact

   Offset = 0 * 10 = 0, so it fetches first page, but page 0 is invalid logically.

3. Final Answer:

   Page number should start from 1, not 0, causing incorrect offset -> Option C

4. Quick Check:

   Page numbering starts at 1 [OK]

Hint: Page numbers start at 1, not 0 [OK]

Common Mistakes:

• Using page 0 as valid page
• Setting limit to zero incorrectly
• Misunderstanding offset calculation

5.

You want to implement cursor-based pagination in Node.js for a real-time chat app. Which approach is best to fetch the next page of messages?

// Current last message ID is stored in lastMessageId
const query = 'SELECT * FROM messages WHERE id < ? ORDER BY id DESC LIMIT ?';
const results = await db.query(query, [lastMessageId, limit]);

Why is this approach better than using offset?

hard

A. Cursor pagination avoids skipping items and handles new data better than offset

B. Offset pagination is faster for real-time data

C. Cursor pagination requires less code but is less reliable

D. Offset pagination works better with unordered data

Solution

1. Step 1: Understand cursor pagination

   Cursor uses a unique ID to fetch next items after the last seen message.

2. Step 2: Compare with offset pagination

   Offset can skip or repeat items if data changes during pagination; cursor avoids this.

3. Final Answer:

   Cursor pagination avoids skipping items and handles new data better than offset -> Option A

4. Quick Check:

   Cursor = stable pagination with changing data [OK]

Hint: Cursor uses last ID to avoid skipping new data [OK]

Common Mistakes:

• Thinking offset is better for real-time data
• Assuming cursor is less reliable
• Confusing cursor with offset usage