Welcome to the final chapter of our complete JavaScript series. In this post, we will explore the Fetch API, which allows us to make API calls, receive data, and utilize it to create interesting applications. By the end of this chapter, we will build a mini project: a currency converter. ## Understanding APIs Before diving into the Fetch API, let's briefly review what an API is. An API, or Application Programming Interface, is a system that allows different software applications to communicate with each other. For example, if you request a pizza recipe from an API, it will return the necessary data to help you prepare that dish. APIs operate on a request-response cycle, where we send a request and receive a response containing the data we need. The Fetch API provides a modern way to make network requests in JavaScript. It is simpler and more powerful than older methods like XMLHttpRequest. The Fetch API returns a promise that resolves to the response of the request. The syntax for using the Fetch API is straightforward: ```javascript fetch(url) .then(response => response.json()) .then(data => console.log(data)); ``` In this example, we send a request to the specified URL, and upon receiving a response, we convert it to JSON format. ## Making API Calls with Fetch To make an API call using the Fetch API, we need to specify the URL of the API endpoint. For instance, if we want to fetch cat facts, we can use the following code: ```javascript const url = 'https://catfact.ninja/fact'; fetch(url) .then(response => response.json()) .then(data => console.log(data)); ``` This code sends a request to the cat facts API and logs the response data to the console. ## Handling Responses When we make a request using the Fetch API, we receive a response object. This object contains various properties, including the status code, headers, and the body of the response. A successful request typically returns a status code of 200. We can access the response body using the `.json()` method, which also returns a promise. ### Example of Handling a Response ```javascript fetch(url) .then(response => { if (!response.ok) { throw new Error('Network response was not ok'); } return response.json(); }) .then(data => console.log(data)) .catch(error => console.error('There was a problem with the fetch operation:', error)); ``` In this example, we check if the response is okay before attempting to parse it as JSON. ## Building a Currency Converter Now that we understand how to make API calls and handle responses, let's apply this knowledge to build a currency converter. This project will allow users to convert amounts from one currency to another using real-time exchange rates. ### Setting Up the Project 1. **HTML Structure**: Create a basic HTML structure with input fields for the amount, dropdowns for selecting currencies, and a button to perform the conversion. 2. **CSS Styling**: Style the application to make it visually appealing. 3. **JavaScript Logic**: Implement the logic to fetch exchange rates and perform conversions. ### Example HTML Structure ```html

Currency Converter

``` ### Fetching Exchange Rates To fetch exchange rates, we can use a public API that provides currency conversion rates. Here’s how we can implement the logic in JavaScript: ```javascript const convertBtn = document.getElementById('convertBtn'); const result = document.getElementById('result'); convertBtn.addEventListener('click', async () => { const amount = document.getElementById('amount').value; const fromCurrency = document.getElementById('fromCurrency').value; const toCurrency = document.getElementById('toCurrency').value; const url = `https://api.exchangerate-api.com/v4/latest/${fromCurrency}`; const response = await fetch(url); const data = await response.json(); const rate = data.rates[toCurrency]; const convertedAmount = (amount * rate).toFixed(2); result.innerText = `${amount} ${fromCurrency} = ${convertedAmount} ${toCurrency}`; }); ``` In this code, we listen for a click event on the convert button, fetch the exchange rates, and calculate the converted amount based on user input. ## Conclusion In this chapter, we explored the Fetch API and learned how to make API calls and handle responses effectively. We applied this knowledge to build a functional currency converter, demonstrating the practical use of JavaScript in real-world applications. As we conclude this series, I hope you found it informative and engaging. Feel free to explore more advanced topics in JavaScript, such as Node.js, React, or other frameworks. Happy coding!