history
doesn't allow this, still you can get history.length
to check if there is history at all (if not - just disable both buttons).
Or you can "dirtyhack" it by wrapping the whole site or app with 100% width|height borderless iframe on your "index" page and log this iframe's hisory "manually" from the top window (not advised at all; will work for the same domain only; will not work with "X-Frame-Options:DENY" on your server).