The Data Validation function I wrote today

<!-- Date Validation -->
// Declaring valid date character, minimum year and maximum year
var dtCh= "/";
var minYear=1900;
var maxYear=2100;

function isInteger(s){
 var i;
    for (i = 0; i < s.length; i++){
        // Check that current character is number.
        var c = s.charAt(i);
        if (((c < "0") || (c > "9"))) return false;
    }
    // All characters are numbers.
    return true;
}

function stripCharsInBag(s, bag){
 var i;
    var returnString = "";
    // Search through string's characters one by one.
    // If character is not in bag, append to returnString.
    for (i = 0; i < s.length; i++){
        var c = s.charAt(i);
        if (bag.indexOf(c) == -1) returnString += c;
    }
    return returnString;
}

function daysInFebruary (year){
 // February has 29 days in any year evenly divisible by four,
    // EXCEPT for centurial years which are not also divisible by 400.
    return (((year % 4 == 0) && ( (!(year % 100 == 0)) || (year % 400 == 0))) ? 29 : 28 );
}
function DaysArray(n) {
 for (var i = 1; i <= n; i++) {
  this[i] = 31
  if (i==4 || i==6 || i==9 || i==11) {this[i] = 30}
  if (i==2) {this[i] = 29}
   }
   return this
}


// dtStr: Date string, format should be YYYY/MM/DD
//dateName: the alert text for date Text(default:"", could also be 'Start Date' or others)
function isDate(dtStr,dateName){
 var daysInMonth = DaysArray(12)
 var pos1=dtStr.indexOf(dtCh)
 var pos2=dtStr.indexOf(dtCh,pos1+1)
 var strYear=dtStr.substring(0,pos1)
 var strMonth=dtStr.substring(pos1+1,pos2)
 var strDay=dtStr.substring(pos2+1)
 if(dateName == null){
  dateName="";
}else{
dateName = dateName + ": ";
}

 strYr=strYear
 if (strDay.charAt(0)=="0" && strDay.length>1) strDay=strDay.substring(1)
 if (strMonth.charAt(0)=="0" && strMonth.length>1) strMonth=strMonth.substring(1)
 for (var i = 1; i <= 3; i++) {
  if (strYr.charAt(0)=="0" && strYr.length>1) strYr=strYr.substring(1)
 }
 month=parseInt(strMonth)
 day=parseInt(strDay)
 year=parseInt(strYr)
 if (pos1==-1 || pos2==-1){
  alert(dateName  +"The date format should be : yyyy/mm/dd")
  return false
 }
 if (strMonth.length<1 || month<1 || month>12){
  alert(dateName  + "Please enter a valid month")
  return false
 }
 if (strDay.length<1 || day<1 || day>31 || (month==2 && day>daysInFebruary(year)) || day > daysInMonth[month]){
  alert(dateName  + "Please enter a valid day")
  return false
 }

 if (strYear.length != 4 || year==0 || year<minYear || year>maxYear){
  alert(dateName  + "Please enter a valid 4 digit year between "+minYear+" and "+maxYear)
  return false
 }
 if (dtStr.indexOf(dtCh,pos2+1)!=-1 || isInteger(stripCharsInBag(dtStr, dtCh))==false){
  alert(dateName  + "Please enter a valid date")
  return false
 }
return true
}

 
  //startDate: Format YYYY/MM/DD
  //checkstartend: whether need to check the start date must not be greater than end date
  // startDateName: the alert text for start date(default: 'Start Date', could also be 'From' or others)
  // endDateName: the alert text for end date(default: 'End Date', could also be 'To' or others)
  function validateDates(startDate,endDate,checkstartend,startDateName,endDateName)
{
if(startDateName == null){
startDateName = "Start Date";
}

if(endDateName == null){
endDateName = "End Date";
}

if(startDate !=null){
     if(isDate(startDate,startDateName) ==false){
        return false;
   }
   }
  
   if(endDate !=null){
     if(isDate(endDate,endDateName) ==false){
        return false;
   }
   }
  
   if(checkstartend){
   if(compareDates(startDate,endDate) == false){
   return false;
   }
   }
  
    return true;
  }
 
  //sFormName: the form name need to validate
  function validateDatesAndForm(startDate,endDate,checkstartend,sFormName,startDateName,endDateName){
   if(validateDates(startDate,endDate,checkstartend,startDateName,endDateName) == true){
   if(sFormName !=null){
     return form2url(sFormName);
   }else{
   return true;
   }
   }else{
   return false;
   }
  }
    //fromDate: format could be YYYY/MM/DD OR YYYY-MM-DD OR OTHER YYYY*MM*DD FORMAT
    function compareDates(fromDate,toDate){
    var yr1  = parseInt(fromDate.substring(0,4),10);
    var mon1 = parseInt(fromDate.substring(5,7),10);
    var dt1  = parseInt(fromDate.substring(8,10),10);
    var yr2  = parseInt(toDate.substring(0,4),10);
    var mon2 = parseInt(toDate.substring(5,7),10);
    var dt2  = parseInt(toDate.substring(8,10),10);
  
    var date1 = new Date();
    date1.setFullYear(yr1, mon1-1, dt1);
    var date2 = new Date();
    date2.setFullYear(yr2, mon2-1, dt2);
    if(date2 < date1)
    {
        alert("Start date cannot be greater than End date");
        return false;
    }
    return true;
}
<!-- end of Data Validation -->