Convert the date time to timestamp and Compare the two datetime (dates) functions in Javascript.

Convert the date time to timestamp in Javascript. similar to strototime() function in php.

// Convert the date time to timestamp in Javascript. similar to strototime() function in php.
function convert_datetime_to_timestamp(date)
{
 var datetime = date.split(" ");
 date = datetime[0];
 time = datetime[1];

 d1 = date.split("-");
 y = d1[0];
 m = d1[1];
 d = d1[2];

 t1 = time.split(":");
 h = t1[0];
 i = t1[1];
 s = t1[2];

 //datetime = m + ' ' + d + ',' + y + ' ' + h + ':' + i + ':'+s;
var date = new Date(y, m, d, h, i, s, '0'); (works both on FireFox and Chrome Browers).
 
 return date.getTime();
}

// Compare the two datetime (dates) in Javascript.

/*  This below function compares two dates with a gap time as 6 Hours.
 @param date1 = '2012-08-06 14:9:19'
 @param date2 = '2012-08-06 20:9:19' 
 @return If errors found, return errors else null (if no errors) found. 
*/
function compare_two_dates(date1, date2)
{
 var error = '';
 
 if ( (date1 != "") || (date2 != "") )
 {
  // Check the dates time here;
  var minutes=1000*60;
  var hours=minutes*60;
  var days=hours*24;
  var years=days*365;
  
  now = new Date();
  current_time= now.getTime();
  
  // Check the dates time here;
  start_time= convert_datetime_to_timestamp(date1);
  expiry_time= convert_datetime_to_timestamp(date2);
  
  gap_hr = 6; // Minimum Gap between two dates is set as 6 Hrs. 
  gap_time= gap_hr*hours;
  diff_time= expiry_time - start_time;
  diff_mm= (diff_time)/minutes;
  diff_hr= Math.round(diff_time/hours);
  
  if ( (current_time >= start_time) && (current_time >= expiry_time))
   error = 'Date Available AND/OR Expiry time should be greater than current time.';

  else if ( (diff_time == 0) || (gap_time > diff_time) )
   error = 'Date Expires should be at least ' + gap_hr + ' hours greater than Date Available time.';
  
  //error = error + ' NowT: '+current_time+' DS: ' + start_time + ' DE: '+ expiry_time+' Diff: ' +diff_time+ ' DMM: ' + diff_mm+ ' DHR: '+diff_hr+' TG: '+gap_time;  
 }
 else {
  error =  'Enter both dates';
 }
 
 return error;
}

For more information about dates, please, check: JavaScript Date Object, JavaScript setDate() Method