Ярослав Астафьев

<form id="xmlUploaderForm" enctype="multipart/form-data">
    <label for="file">Upload file</label>
    <input class="upfile" type="file" name="file">
    <input id="uploadButton" type="button" value="Upload" class="button-primary">
    <span style="padding-left: 20px; display: inline-block;" class="button-spinner"></span>
</form>

$('#uploadButton').click(function(){
        var formData = new FormData($('#xmlUploaderForm')[0]);
        $.ajax({
            url: url,
            type: 'POST',
            xhr: function() {  // Custom XMLHttpRequest
                var myXhr = $.ajaxSettings.xhr();
                return myXhr;
            },
            beforeSend: function(){},
            success: completeHandler,
            error: errorHandler,
            // Form data
            data: formData,
            //Options to tell jQuery not to process data or worry about content-type.
            cache: false,
            contentType: false,
            processData: false
        });
});