What Is AJAX (Asynchronous JavaScript and XML)?

Today, users can expect websites that are fast, smooth, and interactive. No one wants to refresh the entire page every time, only to see the updated information. That is the place where AJAX comes. It is defined as a technique that is used in modern web development to make websites more dynamic and responsive.

AJAX stands for Asynchronous JavaScript and XML. It is not a separate language, it is a combination of different technologies used in web development, like JavaScript, and tools like the XMLHttpRequest object or the fetch() method. In this blog, you will learn what AJAX is, how it works, and some easy AJAX JavaScript examples that help you to understand AJAX.

Table of Contents:

• What is AJAX?
• How AJAX Works?
• How to Use AJAX?
  • Example 1: Basic GET Request
  • Example 2: Basic POST Request
• Difference Between AJAX and JavaScript
• Application of AJAX
• Advantages of Using AJAX
• Limitations of Using AJAX
• Conclusion

What is AJAX?

AJAX stands for Asynchronous JavaScript and XML. It is defined as the technique that allows developers to send and receive data from a server without reloading the full page. This will allow the users to interact with the site while new data is loaded. AJAX uses JavaScript for sending and receiving data from a server. All of this is done through an object called XMLHttpRequest, or the fetch() method.

How AJAX Works?

When you click on a button or type something in the search box, AJAX JavaScript code sends a message to the server asking for the new data. After this, the server will respond with the data, and JavaScript updates that part of the webpage where the change was triggered. Here is how things happen:

• At first, an action will take place, like the user clicks on a button or writes data in the input field.
• Now, a special object is created called XMLHttpRequest. This object is responsible for sending a request to the server by using the GET or POST method.
• After receiving the request, the server will do its job and send the data back to the user.
• The browser uses that data and updates the content without reloading the page.

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How to Use AJAX?

Using AJAX in the code requires basic knowledge of JavaScript. By using the XMLHttpRequest object, you can send and receive requests from the server. Here are the steps to use AJAX JavaScript in the code:

1. At first, create an XMLHttpRequest object, because this object allows your webpage to send and receive data from a server.

let xhttp = new XMLHttpRequest();

2. In the next step, you have to write the function to handle the response sent by the server. Here is the function syntax:

xhttp.onreadystatechange = function() {
  if (this.readyState == 4 && this.status == 200) {
    // Function that handles the response
    document.getElementById("output").innerHTML = this.responseText;
  }
};

Here, readyState == 4 means the request is complete, and status == 200 means the request was successful.

3. Now you have to decide the type of request that you want to send (GET or POST), and then paste the triggered file or web address (URL). 
4. After doing this, you have to send the request by using the send() method.

Example 1: Basic GET Request

let xhttp = new XMLHttpRequest();
xhttp.onreadystatechange = function() {
    if (this.readyState == 4 && this.status == 200) {
        document.getElementById("output").innerHTML = this.responseText;
    }
};
xhttp.open("GET", "data.txt", true);
xhttp.send();

Explanation: In this example, a GET request is sent to the text file called data.txt. When the data comes back, it is shown inside the HTML element with the ID named output.

Example 2: Basic POST Request

let xhttp = new XMLHttpRequest();
xhttp.onreadystatechange = function() {
    if (this.readyState == 4 && this.status == 200) {
        alert("Data sent successfully!");
    }
};
xhttp.open("POST", "submit.php", true);
xhttp.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
xhttp.send("name=John&age=25");

Explanation: In this example, you’re sending the user data to the server by using AJAX JavaScript POST requests. It is used when you are working with login forms or saving user settings. All is done without reloading the page.

Difference Between AJAX and JavaScript

AJAX and JavaScript are not the same. Here are some of the important differences between AJAX and JavaScript:

Application of AJAX

AJAX is an important technique used on many websites and web applications. It helps to make your websites faster and interactive by updating small parts of a page, instead of reloading the full web page.

• AJAX can send the information to the server in the background whenever you fill out a form. This is done without refreshing the page.
• In applications like WhatsApp Web or Facebook Messenger, you can send and receive messages instantly without any delay, only because of AJAX.
• You can get new notifications, messages, and updates in the background because of AJAX JavaScript.

Advantages of Using AJAX

Using Asynchronous JavaScript and XML in a website or web application offers great benefits. Here are some of the advantages of using AJAX in the code:

• With AJAX JavaScript, only some part of the page reloads when the changes are triggered, so the user doesn’t have to wait for a full page reload.
• JavaScript AJAX requests run in the background, so this allows the users to keep interacting with the webpage while the data is being sent.
• Since AJAX calls JavaScript only sends and receives the data that you need. Thus, it uses less internet data and reduces the load on your server.

Limitations of Using AJAX

Here are some of the limitations of using Asynchronous JavaScript and XML in projects:

• The search engines like Google find it difficult to read the content using JavaScript AJAX requests because the data loads in the background.
• Many modern browsers support AJAX, but if anyone uses a very old browser, then this creates issues in the code.
• Working with the code that contains AJAX requires a good internet connection.

Conclusion

AJAX allows webpages to send and receive data from the server in the background. Thus, the whole page doesn’t reload when the content is changed. This makes the websites faster and more user-friendly. Users can search, send forms, filter items, or load more content, without reloading the page, only because of AJAX JavaScript. So, if you want to build efficient websites, then choosing AJAX is the best option.

Looking to prepare for your next tech interview? Check out our comprehensive list of JavaScript Interview Questions to boost your confidence.  

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