Submitting multiple forms with Javascript (no refresh)

I am trying to run this in Chrome/Firefox Console but not having any luck.

(function(d) {
  var form = d.getElementsByTagName('form');
  var i = form.length;

  while (i--) {

    form[i].addEventListener("submit", function(evt){
        evt.preventDefault();
  开发者_Go百科  }, false);

    xhr = new XMLHttpRequest();
    xhr.open("POST", "http://example.com/", true);
    xhr.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");
    xhr.send("media_id=" + form[i].elements["media_id"].value);

  }
})(this.document);

Can anyone spot any problems with it? Thanks

EDIT: I have fixed the problem. Thanks @Niklas

The problem is that you are preventing the form submissions but not actually doing anything to send them. You'd presumably want to add some ajax to send the data.