Dirt simple example

XHR upload.js

function on_file_input_element_changed() {  
        
        var my_file_input_element = my_method_to_find_file_input_element();
        var file = my_file_input_element.files[0];
        var xhr = new XMLHttpRequest();
        var is_async = true;
        xhr.open("POST", "/upload", is_async);
        xhr.setRequestHeader("X-Requested-With", "XMLHttpRequest");
        xhr.setRequestHeader("X-File-Name", encodeURIComponent(file.fileName));
        xhr.setRequestHeader("Content-Type", "application/octet-stream");
        xhr.onreadystatechange = function(){            
            if (xhr.readyState == 4) 
                alert("upload complete!");            
        }
        xhr.send(file);   
}