//Instant Validation with JavaScript-enabled WebDB
  //Listing 3

  //The JavaScript function isCompleteDate checks whether the text entered in a field has 
  //the date format MM/DD/YYYY and appropriate values for month/day/year, displaying an 
  //error message and returning a value of “false” if it does not.

function isCompleteDate(theElement, theName)
{
 // This function checks if the text entered in a field 
 // has the format MM/DD/YYYY. 
 // It also checks if the days and months are valid and
 // if the year is 1500 or later

 var objectName = theName;

 //---- since we need the same functionality for errors ----
 //---- we create a function to simplify error display  ----
 function showError(message)
 {
  alert(objectName + ": " + message);
  theElement.focus();
 }
 
 var date_regex = /^(\d{1,2})\/(\d{1,2})\/(\d{4})$/;
 
 var date_str = theElement.value;

 // ^ indicates start of expression
 // \d{1,2} - the \d means digits and {1,2} means 1 or 2 digits
 // $ indicates end f expression

 if (!date_regex.test(date_str)) 
 {
  showError(theElement.value + " is NOT a valid date");
  theElement.focus();
  return(false);
 }

 //---- separate the month, day and year ----
 var month = RegExp.$1;
 var day = RegExp.$2;
 var year = RegExp.$3;

 if (year < 1500)
 {
  showError(year + " is not a valid year");
  return(false);
 }

 if (month < 1 || month > 12)
 {
  showError(month + " is not a valid month");
  return(false);
 }

 if (day == 0)
 { 
  showError(day + " is not a valid day");
  return(false);
 }

 if ((month == 1 || month == 3 || month == 5 || month == 7 ||
    month == 8 || month == 10 || month == 12) && (day > 31))
 {
  showError(day + " is not a valid day for month " + month);
  return (false) ;
 }

 if ((month == 4 || month == 6 || month == 9 || month == 11) && (day > 30))
 {
  showError(day + " is not a valid day for month " + month);
  return(false);
 } 

 if (month == 2)
 {
  //---- check for leap year -----
  if ((day > 28) && (year%4 != 0)) 
  {
   showError(day + " is not a valid day for month " + month 
         + " of year " + year);
   return(false);
  }

  if ((day > 29) && (year%4 == 0)) 
  {
    showError(day + " is not a valid day for month " + month 
         + " of year " + year);
    return(false);
  }

 }

 return(true);
}