JS code to make POST requests and rewrite current page to the response

http_post_request.js

request = new XMLHttpRequest();
request.open("POST", "http://example.com/", true);
request.setRequestHeader('Content-type', 'application/x-www-form-urlencoded');
request.onreadystatechange = function() {
    if (request.readyState == 4) {
        document.open();
        document.write(request.responseText);
        document.close();
        console.log("done");
    }
};
request.send("param=" + encodeURIComponent("value"));