I need to add a special header to all requests sent using XMLHttpRequest in my project. I achieved this by decorating onreadystatechange the method of XMLHttpRequest:

XMLHttpRequest = new Proxy(XMLHttpRequest, {
    construct: function (target, args) {
        const xhr = new target(...args);
        xhr.onreadystatechange = function () {
            if (xhr.readyState === 1) {
                xhr.setRequestHeader('header name', 'header value');
            }
        };
        return xhr;
    },
});

But it turned out that I don’t need to do this for all urls. I need to determine if the url meets some requirements. And if yes, then add a header to the request, otherwise do not change the request.
If there is a way to get the url to which the request is being made while inside the function that overrides the method onreadystatechange (see the code above)