How Can I Retrieve HTTP Response Headers in JavaScript?

Retrieving HTTP Headers in JavaScript

Accessing the HTTP response headers of a web page can be essential for debugging and analyzing website behavior. Although you cannot directly read the current headers, there are alternative methods to obtain them.

Using the XMLHttpRequest Object

The XMLHttpRequest object offers a way to make asynchronous server requests and retrieve the response headers. Here's how you can use it:

var req = new XMLHttpRequest();
req.open('GET', document.location, true);
req.send(null);
req.onload = function() {
  var headers = req.getAllResponseHeaders().toLowerCase();
  console.log(headers);
};

This code performs a GET request to the current URL, and when the request is complete, it retrieves and displays all the HTTP headers in their lowercase form.

Caveat

It's important to note that making a new request to obtain the headers does not guarantee that the headers will be identical to the current headers. If headers can change dynamically (e.g., after user interaction), they may not be accurate at the time you request them.

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