JavaScript numbers to Words

Question

I\'m trying to convert numbers into english words, for example 1234 would become: \"one thousand two hundred thirty four\".

My Tact

Answer 1

This is a simple ES6+ number to words function. You can simply add 'illions' array to extend digits. American English version. (no 'and' before the end)

// generic number to words

let digits  = ['','one','two','three','four', 'five','six','seven','eight','nine','ten','eleven','twelve','thirteen','fourteen','fifteen','sixteen','seventeen','eighteen','nineteen'];
let ties    = ['', '', 'twenty','thirty','forty','fifty', 'sixty','seventy','eighty','ninety'];
let illions = ['', 'thousand', 'million', 'billion', 'trillion'].reverse()

let join = (a, s) => a.filter(v => v).join(s || ' ')

let tens = s => 
    digits[s] || 
    join([ties[s[0]], digits[s[1]]], '-') // 21 -> twenty-one

let hundreds = s => 
    join(
        (s[0] !== '0' ? [digits[s[0]], 'hundred'] : [])
            .concat( tens(s.substr(1,2)) )  )

let re = '^' + '(\\d{3})'.repeat(illions.length) + '$'

let numberToWords = n => 
    // to filter non number or '', null, undefined, false, NaN
    isNaN(Number(n)) || !n && n !== 0 
        ? 'not a number'
        : Number(n) === 0 
            ? 'zero'  
            : Number(n) >= 10 ** (illions.length * 3)
                ? 'too big'
                : String(n)
                    .padStart(illions.length * 3, '0')
                    .match(new RegExp(re))
                    .slice(1, illions.length + 1)
                    .reduce( (a, v, i) => v === '000' ? a : join([a, hundreds(v), illions[i]]), '')


// just for this question.

let update = () => {
    let value = document.getElementById('number').value
    document.getElementById('container').innerHTML = numberToWords(value)
}