When I use XMLHttpRequest, a file is correctly uploaded using FormData. However, when I switch to jQuery.ajax, my code breaks.

This is the working original code:

function uploadFile(blobFile, fileName) {

    var fd = new FormData();

    fd.append(fileToUpload, blobFile);

    var xhr = new XMLHttpRequest();

    xhr.open(POST, upload.php, true);

    xhr.send(fd);

}

Here is my unsuccessful jQuery.ajax attempt:

function uploadFile(blobFile, fileName) {

    var fd = new FormData();

    fd.append(fileToUpload, blobFile);

    var xm = $.ajax({

        url: upload.php,

        type: POST,

        data: fd,

    });

}

What am I doing wrong? How can I get the file to be uploaded correctly, using AJAX?