1. Introduction

Goal

This tutorial aims to guide you through the process of implementing pagination for large data sets in a REST API.

Learning Objectives

At the end of this tutorial, you will be able to:
- Understand what pagination is and why it's important
- Implement pagination in a REST API
- Use best practices when implementing pagination

Prerequisites

To follow this tutorial, you should have a basic understanding of:
- REST APIs
- JavaScript (specifically Node.js and Express.js)

2. Step-by-Step Guide

What is Pagination?

Pagination is the process of dividing the data into discrete pages, which can be navigated using previous, next, or jump to page functionalities. It's beneficial for improving your API's efficiency and user experience, mainly when working with large data sets.

Implementing Pagination

To implement pagination, you should return a specific number of items (page size) and provide the ability to move forwards and backwards through the pages.

3. Code Examples

Pagination Example

In this example, we will use Express.js, a Node.js framework, to create a simple REST API and implement pagination.

const express = require('express');
const app = express();
const port = 3000;

let data = [];
for(let i=0; i<100; i++) {
  data.push({id: i, name: `Item ${i}`}); // Creating 100 items
}

app.get('/items', (req, res) => {
  const page = parseInt(req.query.page); // page number
  const limit = parseInt(req.query.limit); // number of items per page
  const startIndex = (page - 1) * limit; // calculate start index
  const endIndex = page * limit;

  const result = data.slice(startIndex, endIndex); // get items for the requested page
  res.json(result);
});

app.listen(port, () => console.log(`App listening on port ${port}!`));

In the code above, we are:
- Creating an express app
- Generating 100 items for our data set
- Setting up a route /items which accepts two query parameters: page and limit
- Calculating the start and end index for slicing our data array
- Returning the sliced data array, which corresponds to the requested page

You can run this server and access http://localhost:3000/items?page=2&limit=10 in your browser. You should see items from 10 to 19 (1-indexed).

4. Summary

In this tutorial, we have learned:
- What pagination is and why it's important
- How to implement pagination in a REST API using Express.js

To expand your knowledge, you can learn how to:
- Add error handling (e.g., for requests for non-existing pages)
- Implement sorting or filtering together with pagination

5. Practice Exercises

1. Modify the API to return the total number of pages and the current page in the response.
2. Implement a "previous" and "next" link in the response to help the client navigate between pages.
3. Add error handling for requests for non-existing pages.

Remember, practice is key to mastering any concept. Happy coding!