How to create a Alphanumeric Serial Number in Javascript? -

i trying create alphanumeric serial number in javascript, serial number governed following rules:

1. 3-digit alphanumeric series
2. allowed values 1-9 (zero excluded) , a-z (all capitals exclusions of , o)
3. the code should able give next number after getting input number.

the last part tricky, code fetch existing value of serial number , give output next number.

for example: if input number 11d output number should 11e. please let me know if description enough explain requirement.

the excel sheet same attached here

also part of code script fetch starting value 11d code:

cur_frm.add_fetch('item_group','serial_number','serial_number'); 

    var alphabet = "123456789abcdefghjklmnpqrstuvwxyz";     var alphabetlen = alphabet.length;      function nextdigit(digit) {         nextdigitpos = (alphabet.indexof(digit)+1) % alphabetlen;         return alphabet.charat(nextdigitpos);     }      /**      * computes next serial id.      * @param id id compute successor of,      *        if null or empty string first id      *        "111" returned.      */     function nextserial(id) {         if(id==null || id.length==0) return "111";         var digits = id.split("");         digits[2] = nextdigit(digits[2]);         if(digits[2] == "1") /* overflow */ {             digits[1] = nextdigit(digits[1]);             if(digits[1] == "1") /* overflow */ {                  digits[0] = nextdigit(digits[0])             }         }         return digits.join("");     }