To create a REST API with Node.js, use Express.js to set up the server, define routes for your resources, and implement CRUD operations. Start by installing Express and setting up your endpoints.

Building a REST API using Node.js is a common task for developers looking to create backend services for web applications. In this comprehensive guide, we'll go through the steps necessary to create a simple REST API using Node.js and Express.js:

1. Understanding REST: REST (Representational State Transfer) is an architectural style for designing networked applications. It relies on stateless communication and standard HTTP methods (GET, POST, PUT, DELETE) to perform operations on resources.

2. Setting Up Your Environment: Before you start coding, ensure you have Node.js and npm installed. Create a new directory for your project:

   mkdir my-rest-api
   cd my-rest-api
   npm init -y
   

3. Installing Express: Express is a minimalist web framework for Node.js that makes it easy to build APIs. Install it using npm:

   npm install express
   

4. Creating Your Server: In your project directory, create a new file named server.js. This file will contain your server code:

   const express = require('express');
   const app = express();
   const PORT = process.env.PORT || 3000;
   
   app.use(express.json()); // Middleware for parsing JSON bodies
   
   app.listen(PORT, () => {
       console.log(`Server is running on port ${PORT}`);
   });
   

   This sets up a basic Express server that listens on port 3000.

5. Defining Routes: REST APIs are built around resources. Let's define routes for a simple resource, like items:

   // Get all items
   app.get('/items', (req, res) => {
       // Logic to get items
   });
   
   // Create a new item
   app.post('/items', (req, res) => {
       // Logic to create an item
   });
   
   // Update an item
   app.put('/items/:id', (req, res) => {
       // Logic to update an item
   });
   
   // Delete an item
   app.delete('/items/:id', (req, res) => {
       // Logic to delete an item
   });
   

   Each route corresponds to a CRUD operation on the items resource.

6. Implementing CRUD Operations: Within each route, implement the logic to interact with your data storage (e.g., a database or in-memory array). For example, to create an item:

   let items = [];
   
   app.post('/items', (req, res) => {
       const newItem = req.body;
       items.push(newItem);
       res.status(201).send(newItem);
   });
   

   You can follow a similar pattern for the other CRUD operations, ensuring to handle errors appropriately.

7. Testing Your API: Use tools like Postman or cURL to test your API endpoints. Ensure that each operation (GET, POST, PUT, DELETE) functions as expected.

8. Conclusion: You’ve successfully created a REST API using Node.js and Express. This API can be expanded with more complex functionality, authentication, and error handling as your application grows.