Javascript : how to send AJAX with dataType as script?

Javascript : how to send AJAX with dataType as script?

im trying to create own POST request. Here is my function:
function sendPost(o) {
var h = new XMLHttpRequest();
h.onreadystatechange = requestComplete;
function requestComplete() {
if ( h.readyState === 4 ) {
if ( h.status === 200 ) {
if ( o.done ) {
o.done(h.responseText);
}
} else {
if ( o.fail ) {
o.fail(h.responseText);
}
}
}
}
h.open('POST', o.url, true);
h.setRequestHeader('Content-type', 'application/x-www-form-urlencoded');
h.send(o.data);
}
Everything is OK, but im confused, how to set its dataType to script, like
in jQuery:
$.ajax({
url: 'someurl.php',
type: 'POST',
dataType: 'script' // <-- how to do this?
});