This worked for me (it needs formData support):
<script>
//Load form
var formData = new FormData();
formData.append("param_name1", "param_content1");
formData.append("param_name2", "param_content2");
formData.append("param_nameN", "param_contentN");
//Send form via AJAX
var xhr = new XMLHttpRequest();
xhr.open("POST", YOUR_URL);
xhr.send(formData);
</script>