javascript檢查字串是否為有效日期

/*----------------*//*** DHTML date validation script. Courtesy of SmartWebby.com (http://www.smartwebby.com/dhtml/)*/// Declaring valid date character, minimum year and maximum yearvar 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")       return false   }   if (strDay.length<1 || day<1 || day>31 || (month==2 && day>daysInFebruary(year)) || day > daysInMonth[month]){       alert("Please enter a valid day")       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}