Convert numbers to Words - for Bangladesh

Convert numbers to Words - for Bangladesh.js

/** 
*  Function:   convert_number 
*
*  Description: 
*  Converts a given integer (in range [0..1T-1], inclusive) into 
*  alphabetical format ("one", "two", etc.)
*
*  @int
*
*  @return string
*
*/ 

function convert_number(number) {
        if ((number < 0) || (number > 999999999)) {
            throw new Error("Number is out of range");
        }
        let Kt = Math.floor(number / 10000000); // Koti */
        number -= Kt * 10000000;
        let Gn = Math.floor(number / 100000);  //* lakh  */ 
        number -= Gn * 100000;
        let kn = Math.floor(number / 1000);     //* Thousands (kilo) */ 
        number -= kn * 1000;
        let Hn = Math.floor(number / 100);      //* Hundreds (hecto) */ 
        number -= Hn * 100;
        let Dn = Math.floor(number / 10);       //* Tens (deca) */ 
        let n = number % 10;               /* Ones */

        let res = "";

        if (Kt) {
            res += convert_number(Kt) + " Koti ";
        }
        if (Gn) {
            res += convert_number(Gn) + " Lakh ";
        }

        if (kn) {
            res += (res.length === 0 ? "" : " ") +
                convert_number(kn) + " Thousand";
        }

        if (Hn) {
            // arr.length === 0
            res += (res.length === 0 ? "" : " ") +
                convert_number(Hn) + " Hundred";
        }

        let ones = ["", "One", "Two", "Three", "Four", "Five", "Six",
            "Seven", "Eight", "Nine", "Ten", "Eleven", "Twelve", "Thirteen",
            "Fourteen", "Fifteen", "Sixteen", "Seventeen", "Eightteen",
            "Nineteen"];
        let tens = ["", "", "Twenty", "Thirty", "Fourty", "Fifty", "Sixty",
            "Seventy", "Eigthy", "Ninety"];

        if (Dn || n) {
            if (res !== "") {
                res += " and ";
            }
            if (Dn < 2) {
                res += ones[Dn * 10 + n];
            }
            else {
                res += tens[Dn];

                if (n) {
                    res += "-" + ones[n];
                }
            }
        }

        if (res == null) {
            res = "zero";
        }

        return res;
}

This is modified into JavaScript from this PHP Version
Inspiration by @techjewel