Download and href values does not get updated on callback

Even though I have a callback to update the download and href values of my button, it does not seem to get updated on page load. Can anyone help me?

This is how my button looks:

                        html.A(html.Button('Export Data'), 
                        id = 'download2',
                        download = "", 
                        href = "", 
                        target = "_blank",
                        style = {'height': '36px', 'display': 'inline-grid', 'text-decoration':'none', 'float':'right', }),
                style = {'width': '8%', 'height': '36px', 'display': 'inline-grid', 'margin-right': '20px', 'overflow-y':'auto', 'float':'right', }),