Date Validation using Javascript

Here is the validation for date using javascript.

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;
}

function isDate(dtStr){
    var daysInMonth = DaysArray(12);
    var pos1=dtStr.indexOf(dtCh);
    var pos2=dtStr.indexOf(dtCh,pos1+1);
    var strMonth=dtStr.substring(0,pos1);
    var strDay=dtStr.substring(pos1+1,pos2);
    var strYear=dtStr.substring(pos2+1);
    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("The date format should be : mm/dd/yyyy");
        return false;
    }
    if (strMonth.length<1 || month<1 || month>12){
        alert("Please enter a valid month");
        document.form1.month.focus();
        return false;
    }
    if (strDay.length<1 || day<1 || day>31 || (month==2 && day>daysInFebruary(year)) || day > daysInMonth[month]){
        alert("Please enter a valid day");
        document.form1.day.focus();
        return false;
    }
    if (strYear.length != 4 || year==0 || year<minYear || year>maxYear){
        alert("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("Please enter a valid date");
        return false;
    }
    return true;
}

To check the given string is a Date or not, the date format should be checked as shown below.

var dt = document.form1.month.value +'/' +document.form1.day.value +'/'+ document.form1.year.value;
    if (isDate(dt)==false){
        return false;
    }

The date format to be passed is MM/DD/YYYY.