POST JSON Data using JavaScript

Why is my code not sending the data to server ? It does display the data into the console but doesn't seem to be sending anything.

document.querySelector("form").addEventListener("submit", function (e) {
            e.preventDefault();

            var formData = {
            "name": e.target.elements.name.value,
            "author": e.target.elements.author.value,
            "link": e.target.elements.link.value
            }

            var req = new XMLHttpRequest();

            req.open("POST", "http://localhost/javascript-web-srv/post_form.php", true);
            req.setRequestHeader("Content-Type", "application/json");

            req.send(formData);

            formData = JSON.stringify(formData);

            console.log(formData);

        });