CRM 2011 Generate Year and Month In 4 Character

*Note generate date and year as eg:1209

function GenerateAutoNumYYMM() {

var newvalueMonth;
var d = new Date();  //Today Date
var valueMonth = new Date().getMonth() + 1;  //Value month need to +1
var valueYear = new Date().getFullYear();

var valueYearLength = valueYear.toString().length; //Get the length
var YearToString = valueYear.toString(); //Convert to string

var last_char=YearToString.charAt(valueYearLength-1);  //Get last character
var Before_last_char=YearToString.charAt(valueYearLength-2);  //Get last second character

var LastTwoYearChar = Before_last_char + last_char; //Get last two character

var valueMonthLength = valueMonth.toString().length; //get month length
 
if (valueMonthLength != 2) {
newvalueMonth = "0" + valueMonth.toString(); //Convert to string
}
else {
newvalueMonth = valueMonth.toString(); //Convert to string
}

var NewYYMM = LastTwoYearChar + newvalueMonth; //Combine both month and year
        //Eg. Year 2012 month 9

return NewYYMM; //Answer 1209
}

The reason why im doing this because it is needed for auto numbering year format. Requested in other way.