Javascript Convert Date To String (Past Tense)

/*
 * produces textual output ex '5 hours ago' from string formatted:
 * alert( dateStringPastTense('2007-08-20 10:34:01 pm') );
 * alert( dateStringPastTense('2009-02-20 14:34:23'   ) );
 * alert( dateStringPastTense('08/20/2008 11:29:43 pm') );
 * alert( dateStringPastTense('08/20/2008 23:29:55'   ) );
 */
function dateStringPastTense(date_input)
{
        var dtpieces = date_input.split(" ");
        var dpieces_his = dtpieces[1].split(":");
        var dpieces_ymd = dtpieces[0].split("-");
        if (dpieces_ymd == dtpieces[0])
        {
                var dpieces_mdy = dtpieces[0].split("/");
                dpieces_ymd[0] = dpieces_mdy[2];
                dpieces_ymd[1] = dpieces_mdy[0];
                dpieces_ymd[2] = dpieces_mdy[1];
        }
        if (dtpieces[2] && dtpieces[2].toLowerCase()=='pm')
        {
                dpieces_his[0]=dpieces_his[0]*1 + 12;
        }
        dpieces_ymd[1]-=1;
 
        var d = new Date();
        d.setFullYear( dpieces_ymd[0], dpieces_ymd[1], dpieces_ymd[2] );
        d.setHours   ( dpieces_his[0], dpieces_his[1], dpieces_his[2] );
 
        var sec = (new Date()).getTime() - d.getTime();
        sec/=1000;
 
        if (sec <0)
        {
            return "in future";
        }
        var string_def = {'second':60,'minute':60,'hour':24,'day':30,'month':12,'year':1000};
        for(def in string_def)
        {
                if (sec < string_def[def])
                {
                        return sec + " " + def + (sec>1? "s" : "")+ " ago";
                }
                sec= Math.floor( sec/string_def[def] );
        }
        return "over 1000 years ago";
}