All About APIs (With a Practical Example)

API stands for Application Programming Interface, and it refers to a mechanism of communication between two software systems. For example, an API may be used to connect a web application’s back-end server to the front-end client. Communication between these systems involves requests and responses between the server and the client. The endpoints used can be obtained from the API’s documentation.

There are three main API protocols: representational state transfer (REST) APIs, remote procedural call (RPC) APIs, and simple object access protocol (SOAP) APIs. Of these, REST APIs are the most popular due to its flexibility and implementation, ease of integration, support for various data formats including JSON, XML, and plain text, and high scalability.

REST APIs use HTTP requests (GET, PUT, POST, PATCH, DELETE) to access and use data. The response data is typically sent in the body of the HTTP response. Check out this GeeksforGeeks article for information on each of these HTTP requests. The specific endpoints used to make these requests vary between software systems and are defined in the API documentation. For example, the Coinbase exchange rates API can be used to find out the current exchange rates for different currencies. From the API Docs, the HTTP Request (GET https://api.coinbase.com/v2/exchange-rates) takes one optional argument, the currency, as a query parameter.

Specify currencies and press the Get Exchange Rate button to get exchange rates using the Coinbase API

This example uses the JavaScript's fetch to make a GET request to the Coinbase API as shown:

var apiUrl = `https://api.coinbase.com/v2/exchange-rates?currency=${baseCurrency}`;
// Make the API call
fetch(apiUrl)
  .then((response) => response.json())
  .then((data) => {
    // Handle the API response and display the result
    var rate = data.data.rates[convertedCurrency];
    var result = amount * rate;
    document.getElementById("result").innerHTML = 
    `Output: ${amount} ${baseCurrency} equals ${result.toFixed(2)} ${convertedCurrency}`;
})

REST APIs are stateless, meaning they store no data between requests. Therefore, for APIs that require authentication, authentication must be done with every request. API authentication typically involves either authentication tokens or API keys. Due to the simplicity in use, API keys are commonly employed for paid APIs, and are either sent as query parameters or in the request header.

APIs like the Coinbase API used for the demo do not require authentication. Other commonly used free APIs include:

• News API
• Spotify API
• NASA API
• Geo API
• Bored API

…and many more. You can find a list of over 200 free APIs here.

In conclusion, understanding APIs is pivotal in modern software development, where seamless communication between different systems is essential. APIs, or Application Programming Interfaces, act as bridges, facilitating the exchange of data between software components. Whether for enabling data exchange between web applications or accessing diverse functionalities through free APIs, the understanding of APIs is a valuable asset for developers navigating the intricate web of software systems.

Happy coding!