A function that converts a number to words in Turkish

turkish_NumberToWords.js

const turkish_NumberToWords = (number = 0) => {
     /*
     * Assign spelling words in seperate arrays
     */
     const steps = ['', 'bir', 'iki', 'üç', 'dört', 'beş', 'altı', 'yedi', 'sekiz', 'dokuz']
     const tens = ['', 'on', 'yirmi', 'otuz', 'kırk', 'elli', 'altmış', 'yetmiş', 'seksen', 'doksan']
     const hundreds = ['', 'yüz', 'ikiyüz', 'üçyüz', 'dörtyüz', 'beşyüz', 'altıyüz', 'yediyüz', 'sekizyüz', 'dokuzyüz']
     const nS = ['', 'bin', 'milyon', 'milyar', 'trilyon', 'katrilyon', 'kentilyon', 'seksilyon', 'septilyon', 'oktilyon']
     /*
     * Maximum number step is 30
     */
     const max = 30
     /*
     * Completing number if it has step length which are bigger than 3
     */
     const completer = ['', '00', '0']
     /*
     * Variables which hold data temporary 
     */
     let index
     let backer
     let triples
     let result = ''

     /*
     * Combining less-thousands input to words
     * Ex: > turkish_NumberToWords('134')
     *     > 'yüz' + 'otuz' + 'dört'
     */
     const getUntilThousands = triple => `${hundreds[triple[0]]} ${tens[triple[1]]} ${steps[triple[2]]}`
     
     /*
     * Handling string parameter errors before calculation
     */
     const errorHandlers = () => {
         if (number.toString().length > max) {
             throw new RangeError `Girilen hesaplanamayacak kadar çok büyük. Sayı en fazla ${max} basamak olmalıdır`
         }
         if (typeof number != 'string') {
             throw new TypeError('Parametre string olmalıdır')
         }
         for (let index = 0; index < number.length; ++index) {
             console.log(number[index])
             if (number[index] < '0' || number[index] > '9') {
                 throw new Error('Sayı sadece rakamlardan oluşmalıdır')
             }
         }
     }
     errorHandlers()
     
     /*
     * Seperating triples as a word from end edge
     */
     number = completer[number.length % 3] + number
     /*
     * Iterating over seperated triple length
     */
     for ( index = number.length, backer = 0; index > 0; index -= 3, ++backer ) {
         /*
         * Reigstering next triple to calculate
         */
         triples = getUntilThousands(number.substr(index - 3, 3))
         /*
         * If the last triple hasn't reached yet,
         * extend the resulted and combined words to the right
         */
         if (triples !== '') {
             result = `${triples} ${nS[backer]} ${result}`
         }
     }
     /*
     * There is no one thousand or a thousand in turkish,
     * just returning last word
     */
     if (result.substr(0, 7) === 'bir bin') {
         return result.substr(4)
     } else if (result === '') {
         return 'sıfır'
     } else {
         return result
     }
 }