Pagination patterns in Node.js

Introduction

Pagination helps split large data into smaller parts so users can see it page by page. It makes apps faster and easier to use.

Showing a list of products in an online store with many items.

Displaying search results that have hundreds or thousands of entries.

Loading user comments on a blog post without slowing down the page.

Showing messages in a chat app where new messages keep coming.

Fetching data from a database in small chunks to save memory.

Syntax

Node.js

const page = 1; // current page number
const limit = 10; // items per page
const offset = (page - 1) * limit;

// Use offset and limit in database query
const results = await db.query('SELECT * FROM items LIMIT ? OFFSET ?', [limit, offset]);

offset tells where to start fetching data.

limit controls how many items to get per page.

Examples

This fetches the second page with 5 items per page.

Node.js

const page = 2;
const limit = 5;
const offset = (page - 1) * limit;
// Fetch items 6 to 10

This fetches the first page with 20 items.

Node.js

const page = 1;
const limit = 20;
const offset = 0;
// Fetch first 20 items

Cursor pagination uses a marker to fetch next items, useful for real-time data.

Node.js

const cursor = 'abc123';
// Use cursor for cursor-based pagination instead of offset

Sample Program

This Node.js Express app serves a list of 50 items with pagination. You can request pages with query parameters like ?page=2&limit=5. It returns the current page, limit, total items, total pages, and the items for that page.

Node.js

import express from 'express';
const app = express();

const items = Array.from({ length: 50 }, (_, i) => `Item ${i + 1}`);

app.get('/items', (req, res) => {
  const page = Number(req.query.page) || 1;
  const limit = Number(req.query.limit) || 10;
  const offset = (page - 1) * limit;

  const pagedItems = items.slice(offset, offset + limit);

  res.json({
    page,
    limit,
    totalItems: items.length,
    totalPages: Math.ceil(items.length / limit),
    data: pagedItems
  });
});

app.listen(3000, () => {
  console.log('Server running on http://localhost:3000');
});

Important Notes

Always validate page and limit values to avoid errors or too large queries.

Cursor pagination is better for constantly changing data to avoid missing or repeating items.

Use indexes in your database to speed up pagination queries.

Summary

Pagination splits data into pages to improve speed and usability.

Use limit and offset for simple page-based pagination.

Cursor pagination is an alternative for real-time or large datasets.

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