**Course Title:** Mastering Express.js: Building Scalable Web Applications and APIs **Section Title:** Building RESTful APIs **Topic:** Handling API requests and responses (JSON format) ## Introduction In this topic, we'll explore how to handle API requests and responses in JSON format using Express.js. We'll cover the basics of JSON data format, request and response headers, and body parsing using middlewares. By the end of this topic, you'll be able to handle API requests and responses with confidence. ## Understanding JSON Data Format JSON (JavaScript Object Notation) is a lightweight, text-based data interchange format that's widely used for exchanging data between web servers, web applications, and mobile apps. It's human-readable, easy to parse, and supports data types like strings, numbers, booleans, arrays, and objects. For example, here's a simple JSON object: ```json { "name": "John Doe", "age": 30, "city": "New York" } ``` ## Request and Response Headers Request and response headers are key-value pairs that are sent with HTTP requests and responses. They contain metadata about the request or response, such as the content type, cache headers, and authorization tokens. Here are some common request headers: * `Content-Type`: specifies the format of the request body (e.g., `application/json`) * `Accept`: specifies the format of the response data (e.g., `application/json`) * `Authorization`: specifies the authentication token or credentials And here are some common response headers: * `Content-Type`: specifies the format of the response data (e.g., `application/json`) * `Content-Length`: specifies the size of the response body in bytes * `Cache-Control`: specifies caching instructions for the response data ## Body Parsing Using Middlewares Express.js provides several middlewares for parsing request bodies, including: * `express.json()`: parses JSON data in the request body * `express.urlencoded()`: parses URL-encoded data in the request body * `body-parser`: a third-party middleware for parsing request bodies Here's an example of using `express.json()` middleware to parse JSON data in the request body: ```javascript const express = require('express'); const app = express(); app.use(express.json()); // parse JSON data in the request body app.post('/users', (req, res) => { const userData = req.body; // access the parsed JSON data console.log(userData); res.json(userData); // respond with the same data in JSON format }); ``` ## Handling API Requests and Responses To handle API requests and responses in Express.js, you'll need to define routes for each API endpoint. Here's an example of handling a `GET` request to retrieve a list of users: ```javascript app.get('/users', (req, res) => { const users = [ { id: 1, name: 'John Doe' }, { id: 2, name: 'Jane Doe' }, ]; res.json(users); // respond with the user data in JSON format }); ``` And here's an example of handling a `POST` request to create a new user: ```javascript app.post('/users', (req, res) => { const userData = req.body; console.log(userData); // create a new user object and save it to the database const user = { id: 3, name: userData.name }; res.json(user); // respond with the newly created user data }); ``` ## Key Takeaways * JSON is a lightweight, text-based data interchange format used for exchanging data between web servers, web applications, and mobile apps. * Request and response headers contain metadata about the request or response, such as content type and caching instructions. * Express.js provides middlewares for parsing request bodies, including `express.json()` and `body-parser`. * Define routes for each API endpoint to handle API requests and responses. * Use `res.json()` to respond with data in JSON format. ## Practical Exercise Create an API endpoint to handle a `GET` request to retrieve a list of products. Use `express.json()` middleware to parse JSON data in the request body. Define a route for the API endpoint and use `res.json()` to respond with the product data. **Example Use Case:** Create a RESTful API for an e-commerce platform to retrieve product information. **External Resources:** * [JSON official website](https://www.json.org/) * [Express.js documentation on request and response](https://expressjs.com/en/4x/api.html#req) * [Body-parser middleware](https://www.npmjs.com/package/body-parser) **Leave a Comment or Ask for Help** If you have any questions or need further clarification on handling API requests and responses in Express.js, please leave a comment below or ask for help in the [contact page](https://[Your Website URL]/contact). **What's Next?** In the next topic, we'll cover implementing versioning for APIs. We'll discuss the benefits of versioning, common versioning strategies, and how to implement versioning using Express.js. Proceed to the next topic: [Implementing versioning for APIs](#).