Asynchronous Programming - (AJAX Tutorial)

Asynchronous programming is a way of writing code where a program can continue to execute other tasks while waiting for a slow task to finish. AJAX (Asynchronous JavaScript and XML) is a popular technique that uses asynchronous programming to update the contents of a web page without the need to reload the entire page. In this tutorial, we'll go over the syntax, example, output, explanation, use, important points, and summary of asynchronous programming using AJAX.

Syntax

var xhttp = new XMLHttpRequest();
xhttp.onreadystatechange = function() {
    if (this.readyState == 4 && this.status == 200) {
        // Do something with the response
    }
};
xhttp.open("GET", "url", true);
xhttp.send();

Example

Let's use AJAX to retrieve data from a server and display it on a web page without the need to reload the entire page.

// Create an XMLHttpRequest object
var xhttp = new XMLHttpRequest();

// Set the function to be called when the state changes
xhttp.onreadystatechange = function() {
    // Check the state and status
    if (this.readyState == 4 && this.status == 200) {
        // Update the contents of a div element with the response
        document.getElementById("demo").innerHTML = this.responseText;
    }
};

// Open the XMLHttpRequest object and send the request
xhttp.open("GET", "myData.txt", true);
xhttp.send();

Explanation

In this example, we used AJAX to retrieve data from a server and display it on a web page without the need to reload the entire page. We first created an XMLHttpRequest object using the new keyword. We then set the function to be called when the state of the object changes using the onreadystatechange property. Inside the function, we checked if the state was equal to 4 (meaning that the response has been received) and the status was equal to 200 (meaning that the request was successful). If so, we updated the contents of a div element with the response using the innerHTML property. Finally, we opened the XMLHttpRequest object using the open() method and sent the request using the send() method.

Use

The main use of asynchronous programming using AJAX is to update the contents of a web page without the need to reload the entire page. This can improve the user experience by making the web page feel more responsive and reducing the amount of data that needs to be transferred between the client and server.

Important Points

• AJAX requests are asychronous by default, meaning that the program can continue to run other tasks while waiting for the request to complete.
• The XMLHttpRequest object is used to send and receive data from a server using AJAX.
• The open() method is used to open an AJAX request and the send() method is used to send the request to the server.
• The onreadystatechange property can be used to set a function to be called when the state of the XMLHttpRequest object changes.
• The response from the server can be accessed using the responseText property.

Summary

In this tutorial, we discussed asynchronous programming using AJAX. We covered the syntax, example, output, explanation, use, and important points of AJAX requests. With this knowledge, you can now use AJAX to update the contents of a web page without the need to reload the entire page.