HTTP HEAD Request - JavaScript/Ajax Implementation
The Hypertext Transfer Protocol (HTTP) is a fundamental protocol used for communication between web servers and clients. It allows for the transfer of data, such as HTML documents, images, and videos, over the internet.
One of the most commonly used HTTP requests is the HEAD request. This request is used to retrieve the header information of a particular resource without actually downloading the entire content. In this article, we will explore how to implement a HTTP HEAD request using JavaScript and Ajax.
First, let's understand the purpose of a HEAD request. When a client makes a request for a resource, the server responds with the full content of that resource. However, in some cases, the client might only need to retrieve the header information, such as the content type, content length, and last modified date. This is where the HEAD request comes in handy, as it saves bandwidth and reduces the server load by not sending the entire content.
To make a HEAD request using JavaScript, we will use the XMLHttpRequest object, also known as Ajax. This object allows us to make HTTP requests from a web page without the need to reload the entire page. To create an XMLHttpRequest object, we can use the following code:
var xhttp = new XMLHttpRequest();
Next, we need to specify the type of request we want to make, in this case, a HEAD request. We can do this by using the open() method and passing in the type of request, the URL of the resource, and a boolean value indicating whether the request should be asynchronous or not.
xhttp.open("HEAD", "https://www.example.com/resource", true);
Now, we need to define a function that will be called when the server responds to our request. We can do this by using the onreadystatechange event and checking if the readyState property is equal to 4, which indicates that the request has been completed and the response is ready.
xhttp.onreadystatechange = function() {
if (this.readyState == 4) {
// code to handle the response
}
};
Inside the function, we can access the response headers by using the getResponseHeader() method and passing in the name of the header we want to retrieve. For example, to get the content type, we can use the following code:
var contentType = xhttp.getResponseHeader("Content-Type");
We can then use this information to perform any necessary actions, such as displaying the content type to the user.
Now, let's see how we can implement a HEAD request using Ajax. First, we will create a simple HTML page with a button that will trigger the request and a container to display the response.
<html>
<head>
<script>
// code for the HTTP HEAD request
</script>
</head>
<body>
<button onclick="makeHeadRequest()">Make HEAD Request</button>
<div id="response"></div>
</body>
</html>
Next, we will write the JavaScript code to make the request and handle the response.
