Convert digits into words with JavaScript

Question

I am making a code which converts the given amount into words, heres is what I have got after googling. But I think its a little lengthy code to achieve a simple task. Two Regular Expressions and two for loops, I want something simpler.

I am trying to make it as shorter as possible. and will post what I come up with

Any suggestions?

var th = ['','thousand','million', 'billion','trillion'];
var dg = ['zero','one','two','three','four', 'five','six','seven','eight','nine'];
 var tn = ['ten','eleven','twelve','thirteen', 'fourteen','fifteen','sixteen', 'seventeen','eighteen','nineteen'];
 var tw = ['twenty','thirty','forty','fifty', 'sixty','seventy','eighty','ninety'];

function toWords(s) {
    s = s.toString();
    s = s.replace(/[\, ]/g,'');
    if (s != parseFloat(s)) return 'not a number';
    var x = s.indexOf('.');
    if (x == -1)
        x = s.length;
    if (x > 15)
        return 'too big';
    var n = s.split(''); 
    var str = '';
    var sk = 0;
    for (var i=0;   i < x;  i++) {
        if ((x-i)%3==2) { 
            if (n[i] == '1') {
                str += tn[Number(n[i+1])] + ' ';
                i++;
                sk=1;
            } else if (n[i]!=0) {
                str += tw[n[i]-2] + ' ';
                sk=1;
            }
        } else if (n[i]!=0) { // 0235
            str += dg[n[i]] +' ';
            if ((x-i)%3==0) str += 'hundred ';
            sk=1;
        }
        if ((x-i)%3==1) {
            if (sk)
                str += th[(x-i-1)/3] + ' ';
            sk=0;
        }
    }

    if (x != s.length) {
        var y = s.length;
        str += 'point ';
        for (var i=x+1; i<y; i++)
            str += dg[n[i]] +' ';
    }
    return str.replace(/\s+/g,' ');
}

Also, the above code converts to English numbering system like Million/Billion, I wan't South Asian numbering system. like in Lakhs and Crores

Answer 1

You can check my version from github. It is not so hard way. I test this for the numbers between 0 and 9999, but you can extend array if you would like digits to words

Answer 2

"Deceptively simple task." – Potatoswatter

Indeed. There's many little devils hanging out in the details of this problem. It was very fun to solve tho.

EDIT: This update takes a much more compositional approach. Previously there was one big function which wrapped a couple other proprietary functions. Instead, this time we define generic reusable functions which could be used for many varieties of tasks. More about those after we take a look at numToWords itself …

// numToWords :: (Number a, String a) => a -> String
let numToWords = n => {
  let a = [
    '', 'one', 'two', 'three', 'four',
    'five', 'six', 'seven', 'eight', 'nine',
    'ten', 'eleven', 'twelve', 'thirteen', 'fourteen',
    'fifteen', 'sixteen', 'seventeen', 'eighteen', 'nineteen'
  ];
  let b = [
    '', '', 'twenty', 'thirty', 'forty',
    'fifty', 'sixty', 'seventy', 'eighty', 'ninety'
  ];
  let g = [
    '', 'thousand', 'million', 'billion', 'trillion', 'quadrillion',
    'quintillion', 'sextillion', 'septillion', 'octillion', 'nonillion'
  ];
  // this part is really nasty still
  // it might edit this again later to show how Monoids could fix this up
  let makeGroup = ([ones,tens,huns]) => {
    return [
      num(huns) === 0 ? '' : a[huns] + ' hundred ',
      num(ones) === 0 ? b[tens] : b[tens] && b[tens] + '-' || '',
      a[tens+ones] || a[ones]
    ].join('');
  };
  // "thousands" constructor; no real good names for this, i guess
  let thousand = (group,i) => group === '' ? group : `${group} ${g[i]}`;
  // execute !
  if (typeof n === 'number') return numToWords(String(n));
  if (n === '0')             return 'zero';
  return comp (chunk(3)) (reverse) (arr(n))
    .map(makeGroup)
    .map(thousand)
    .filter(comp(not)(isEmpty))
    .reverse()
    .join(' ');
};

Here are the dependencies:

You'll notice these require next to no documentation because their intents are immediately clear. chunk might be the only one that takes a moment to digest, but it's really not too bad. Plus the function name gives us a pretty good indication what it does, and it's probably a function we've encountered before.

const arr = x => Array.from(x);
const num = x => Number(x) || 0;
const str = x => String(x);
const isEmpty = xs => xs.length === 0;
const take = n => xs => xs.slice(0,n);
const drop = n => xs => xs.slice(n);
const reverse = xs => xs.slice(0).reverse();
const comp = f => g => x => f (g (x));
const not = x => !x;
const chunk = n => xs =>
  isEmpty(xs) ? [] : [take(n)(xs), ...chunk (n) (drop (n) (xs))];

"So these make it better?"

Look at how the code has cleaned up significantly

// NEW CODE (truncated)
return comp (chunk(3)) (reverse) (arr(n))
    .map(makeGroup)
    .map(thousand)
    .filter(comp(not)(isEmpty))
    .reverse()
    .join(' ');

// OLD CODE (truncated)
let grp = n => ('000' + n).substr(-3);
let rem = n => n.substr(0, n.length - 3);
let cons = xs => x => g => x ? [x, g && ' ' + g || '', ' ', xs].join('') : xs;
let iter = str => i => x => r => {
  if (x === '000' && r.length === 0) return str;
  return iter(cons(str)(fmt(x))(g[i]))
             (i+1)
             (grp(r))
             (rem(r));
};
return iter('')(0)(grp(String(n)))(rem(String(n)));

Most importantly, the utility functions we added in the new code can be used other places in your app. This means that, as a side effect of implementing numToWords in this way, we get the other functions for free. Bonus soda !

Some tests

console.log(numToWords(11009));
//=> eleven thousand nine

console.log(numToWords(10000001));
//=> ten million one 

console.log(numToWords(987));
//=> nine hundred eighty-seven

console.log(numToWords(1015));
//=> one thousand fifteen

console.log(numToWords(55111222333));
//=> fifty-five billion one hundred eleven million two hundred 
//   twenty-two thousand three hundred thirty-three

console.log(numToWords("999999999999999999999991"));
//=> nine hundred ninety-nine sextillion nine hundred ninety-nine
//   quintillion nine hundred ninety-nine quadrillion nine hundred
//   ninety-nine trillion nine hundred ninety-nine billion nine
//   hundred ninety-nine million nine hundred ninety-nine thousand
//   nine hundred ninety-one

console.log(numToWords(6000753512));
//=> six billion seven hundred fifty-three thousand five hundred
//   twelve 

Runnable demo

const arr = x => Array.from(x);
const num = x => Number(x) || 0;
const str = x => String(x);
const isEmpty = xs => xs.length === 0;
const take = n => xs => xs.slice(0,n);
const drop = n => xs => xs.slice(n);
const reverse = xs => xs.slice(0).reverse();
const comp = f => g => x => f (g (x));
const not = x => !x;
const chunk = n => xs =>
  isEmpty(xs) ? [] : [take(n)(xs), ...chunk (n) (drop (n) (xs))];

// numToWords :: (Number a, String a) => a -> String
let numToWords = n => {
  
  let a = [
    '', 'one', 'two', 'three', 'four',
    'five', 'six', 'seven', 'eight', 'nine',
    'ten', 'eleven', 'twelve', 'thirteen', 'fourteen',
    'fifteen', 'sixteen', 'seventeen', 'eighteen', 'nineteen'
  ];
  
  let b = [
    '', '', 'twenty', 'thirty', 'forty',
    'fifty', 'sixty', 'seventy', 'eighty', 'ninety'
  ];
  
  let g = [
    '', 'thousand', 'million', 'billion', 'trillion', 'quadrillion',
    'quintillion', 'sextillion', 'septillion', 'octillion', 'nonillion'
  ];
  
  // this part is really nasty still
  // it might edit this again later to show how Monoids could fix this up
  let makeGroup = ([ones,tens,huns]) => {
    return [
      num(huns) === 0 ? '' : a[huns] + ' hundred ',
      num(ones) === 0 ? b[tens] : b[tens] && b[tens] + '-' || '',
      a[tens+ones] || a[ones]
    ].join('');
  };
  
  let thousand = (group,i) => group === '' ? group : `${group} ${g[i]}`;
  
  if (typeof n === 'number')
    return numToWords(String(n));
  else if (n === '0')
    return 'zero';
  else
    return comp (chunk(3)) (reverse) (arr(n))
      .map(makeGroup)
      .map(thousand)
      .filter(comp(not)(isEmpty))
      .reverse()
      .join(' ');
};


console.log(numToWords(11009));
//=> eleven thousand nine

console.log(numToWords(10000001));
//=> ten million one 

console.log(numToWords(987));
//=> nine hundred eighty-seven

console.log(numToWords(1015));
//=> one thousand fifteen

console.log(numToWords(55111222333));
//=> fifty-five billion one hundred eleven million two hundred 
//   twenty-two thousand three hundred thirty-three

console.log(numToWords("999999999999999999999991"));
//=> nine hundred ninety-nine sextillion nine hundred ninety-nine
//   quintillion nine hundred ninety-nine quadrillion nine hundred
//   ninety-nine trillion nine hundred ninety-nine billion nine
//   hundred ninety-nine million nine hundred ninety-nine thousand
//   nine hundred ninety-one

console.log(numToWords(6000753512));
//=> six billion seven hundred fifty-three thousand five hundred
//   twelve

---

You can transpile the code using babel.js if you want to see the ES5 variant

Answer 3

var inWords = function(totalRent){
//console.log(totalRent);
var a = ['','one ','two ','three ','four ', 'five ','six ','seven ','eight ','nine ','ten ','eleven ','twelve ','thirteen ','fourteen ','fifteen ','sixteen ','seventeen ','eighteen ','nineteen '];
var b = ['', '', 'twenty','thirty','forty','fifty', 'sixty','seventy','eighty','ninety'];
var number = parseFloat(totalRent).toFixed(2).split(".");
var num = parseInt(number[0]);
var digit = parseInt(number[1]);
//console.log(num);
if ((num.toString()).length > 9)  return 'overflow';
var n = ('000000000' + num).substr(-9).match(/^(\d{2})(\d{2})(\d{2})(\d{1})(\d{2})$/);
var d = ('00' + digit).substr(-2).match(/^(\d{2})$/);;
if (!n) return; var str = '';
str += (n[1] != 0) ? (a[Number(n[1])] || b[n[1][0]] + ' ' + a[n[1][1]]) + 'crore ' : '';
str += (n[2] != 0) ? (a[Number(n[2])] || b[n[2][0]] + ' ' + a[n[2][1]]) + 'lakh ' : '';
str += (n[3] != 0) ? (a[Number(n[3])] || b[n[3][0]] + ' ' + a[n[3][1]]) + 'thousand ' : '';
str += (n[4] != 0) ? (a[Number(n[4])] || b[n[4][0]] + ' ' + a[n[4][1]]) + 'hundred ' : '';
str += (n[5] != 0) ? (a[Number(n[5])] || b[n[5][0]] + ' ' + a[n[5][1]]) + 'Rupee ' : '';
str += (d[1] != 0) ? ((str != '' ) ? "and " : '') + (a[Number(d[1])] || b[d[1][0]] + ' ' + a[d[1][1]]) + 'Paise ' : 'Only!';
console.log(str);
return str;
}

This is modified code supports for Indian Rupee with 2 decimal place.

Answer 4

Though, this question has been answered - still I want to share something I recently developed in java script (based on the logic of an old C#. Net implementation I found in Internet) for converting Indian currency values to Words. It can handle up to 40 digits. You can have a look.

Usage: InrToWordConverter.Initialize();. var inWords = InrToWordConverter.ConvertToWord(amount);

Implementation:

htPunctuation = {};
listStaticSuffix = {};
listStaticPrefix = {};
listHelpNotation = {};

var InrToWordConverter = function () {

};

InrToWordConverter.Initialize = function () {
    InrToWordConverter.LoadStaticPrefix();
    InrToWordConverter.LoadStaticSuffix();
    InrToWordConverter.LoadHelpofNotation();
};

InrToWordConverter.ConvertToWord = function (value) {
    value = value.toString();

    if (value) {
        var tokens = value.split(".");
        var rsPart = "";
        var psPart = "";
        if (tokens.length === 2) {
            rsPart = String.trim(tokens[0]) || "0";
            psPart = String.trim(tokens[1]) || "0";
        }
        else if (tokens.length === 1) {
            rsPart = String.trim(tokens[0]) || "0";
            psPart = "0";
        }
        else {
            rsPart = "0";
            psPart = "0";
        }

        htPunctuation = {};
        var rsInWords = InrToWordConverter.ConvertToWordInternal(rsPart) || "Zero";
        var psInWords = InrToWordConverter.ConvertToWordInternal(psPart) || "Zero";

        var result = "Rupees " + rsInWords + "and " + psInWords + " Paise.";
        return result;
    }
};

InrToWordConverter.ConvertToWordInternal = function (value) {
    var convertedString = "";
    if (!(value.toString().length > 40))
    {
        if (InrToWordConverter.IsNumeric(value.toString()))
        {
            try
            {
                var strValue = InrToWordConverter.Reverse(value);
                switch (strValue.length)
                {
                    case 1:
                        if (parseInt(strValue.toString()) > 0) {
                            convertedString = InrToWordConverter.GetWordConversion(value);
                        }
                        else {
                            convertedString = "Zero ";
                        }
                        break;
                    case 2:
                        convertedString = InrToWordConverter.GetWordConversion(value);
                        break;
                    default:
                        InrToWordConverter.InsertToPunctuationTable(strValue);
                        InrToWordConverter.ReverseHashTable();
                        convertedString = InrToWordConverter.ReturnHashtableValue();
                        break;
                }
            }
            catch (exception) {
                convertedString = "Unexpected Error Occured <br/>";
            }
        }
        else {
            convertedString = "Please Enter Numbers Only, Decimal Values Are not supported";
        }
    }
    else {
        convertedString = "Please Enter Value in Less Then or Equal to 40 Digit";
    }
    return convertedString;
};

InrToWordConverter.IsNumeric = function (valueInNumeric) {
    var isFine = true;
    valueInNumeric = valueInNumeric || "";
    var len = valueInNumeric.length;
    for (var i = 0; i < len; i++) {
        var ch = valueInNumeric[i];
        if (!(ch >= '0' && ch <= '9')) {
            isFine = false;
            break;
        }
    }
    return isFine;
};

InrToWordConverter.ReturnHashtableValue = function () {
    var strFinalString = "";
    var keysArr = [];
    for (var key in htPunctuation) {
        keysArr.push(key);
    }
    for (var i = keysArr.length - 1; i >= 0; i--) {
        var hKey = keysArr[i];
        if (InrToWordConverter.GetWordConversion((htPunctuation[hKey]).toString()) !== "") {
            strFinalString = strFinalString + InrToWordConverter.GetWordConversion((htPunctuation[hKey]).toString()) + InrToWordConverter.StaticPrefixFind((hKey).toString());
        }
    }
    return strFinalString;
};

InrToWordConverter.ReverseHashTable = function () {
    var htTemp = {};
    for (var key in htPunctuation) {
        var item = htPunctuation[key];
        htTemp[key] = InrToWordConverter.Reverse(item.toString());
    }
    htPunctuation = {};
    htPunctuation = htTemp;
};

InrToWordConverter.InsertToPunctuationTable = function (strValue) {
    htPunctuation[1] = strValue.substr(0, 3).toString();
    var j = 2;
    for (var i = 3; i < strValue.length; i = i + 2) {
        if (strValue.substr(i).length > 0) {
            if (strValue.substr(i).length >= 2) {
                htPunctuation[j] = strValue.substr(i, 2).toString();
            }
            else {
                htPunctuation[j] = strValue.substr(i, 1).toString();
            }
        }
        else {
            break;
        }
        j++;

    }
};

InrToWordConverter.Reverse = function (strValue) {
    var reversed = "";
    for (var i in strValue) {
        var ch = strValue[i];
        reversed = ch + reversed;
    }
    return reversed;
};

InrToWordConverter.GetWordConversion = function (inputNumber) {
    var toReturnWord = "";
    if (inputNumber.length <= 3 && inputNumber.length > 0) {
        if (inputNumber.length === 3) {
            if (parseInt(inputNumber.substr(0, 1)) > 0) {
                toReturnWord = toReturnWord + InrToWordConverter.StaticSuffixFind(inputNumber.substr(0, 1)) + "Hundred ";
            }

            var tempString = InrToWordConverter.StaticSuffixFind(inputNumber.substr(1, 2));

            if (tempString === "")
            {
                toReturnWord = toReturnWord + InrToWordConverter.StaticSuffixFind(inputNumber.substr(1, 1) + "0");
                toReturnWord = toReturnWord + InrToWordConverter.StaticSuffixFind(inputNumber.substr(2, 1));
            }
            toReturnWord = toReturnWord + tempString;
        }
        if (inputNumber.length === 2)
        {
            var tempString = InrToWordConverter.StaticSuffixFind(inputNumber.substr(0, 2));
            if (tempString === "")
            {
                toReturnWord = toReturnWord + InrToWordConverter.StaticSuffixFind(inputNumber.substr(0, 1) + "0");
                toReturnWord = toReturnWord + InrToWordConverter.StaticSuffixFind(inputNumber.substr(1, 1));
            }
            toReturnWord = toReturnWord + tempString;
        }
        if (inputNumber.length === 1)
        {
            toReturnWord = toReturnWord + InrToWordConverter.StaticSuffixFind(inputNumber.substr(0, 1));
        }

    }
    return toReturnWord;
};

InrToWordConverter.StaticSuffixFind = function (numberKey) {
    var valueFromNumber = "";
    for (var key in listStaticSuffix) {
        if (String.trim(key.toString()) === String.trim(numberKey)) {
            valueFromNumber = listStaticSuffix[key].toString();
            break;
        }
    }
    return valueFromNumber;
};

InrToWordConverter.StaticPrefixFind = function (numberKey) {
    var valueFromNumber = "";
    for (var key in listStaticPrefix) {
        if (String.trim(key) === String.trim(numberKey)) {
            valueFromNumber = listStaticPrefix[key].toString();
            break;
        }
    }
    return valueFromNumber;
};

InrToWordConverter.StaticHelpNotationFind = function (numberKey) {
    var helpText = "";
    for (var key in listHelpNotation) {
        if (String.trim(key.toString()) === String.trim(numberKey)) {
            helpText = listHelpNotation[key].toString();
            break;
        }
    }
    return helpText;
};

InrToWordConverter.LoadStaticPrefix = function () {
    listStaticPrefix[2] = "Thousand ";
    listStaticPrefix[3] = "Lac ";
    listStaticPrefix[4] = "Crore ";
    listStaticPrefix[5] = "Arab ";
    listStaticPrefix[6] = "Kharab ";
    listStaticPrefix[7] = "Neel ";
    listStaticPrefix[8] = "Padma ";
    listStaticPrefix[9] = "Shankh ";
    listStaticPrefix[10] = "Maha-shankh ";
    listStaticPrefix[11] = "Ank ";
    listStaticPrefix[12] = "Jald ";
    listStaticPrefix[13] = "Madh ";
    listStaticPrefix[14] = "Paraardha ";
    listStaticPrefix[15] = "Ant ";
    listStaticPrefix[16] = "Maha-ant ";
    listStaticPrefix[17] = "Shisht ";
    listStaticPrefix[18] = "Singhar ";
    listStaticPrefix[19] = "Maha-singhar ";
    listStaticPrefix[20] = "Adant-singhar ";
};

InrToWordConverter.LoadStaticSuffix = function () {
    listStaticSuffix[1] = "One ";
    listStaticSuffix[2] = "Two ";
    listStaticSuffix[3] = "Three ";
    listStaticSuffix[4] = "Four ";
    listStaticSuffix[5] = "Five ";
    listStaticSuffix[6] = "Six ";
    listStaticSuffix[7] = "Seven ";
    listStaticSuffix[8] = "Eight ";
    listStaticSuffix[9] = "Nine ";
    listStaticSuffix[10] = "Ten ";
    listStaticSuffix[11] = "Eleven ";
    listStaticSuffix[12] = "Twelve ";
    listStaticSuffix[13] = "Thirteen ";
    listStaticSuffix[14] = "Fourteen ";
    listStaticSuffix[15] = "Fifteen ";
    listStaticSuffix[16] = "Sixteen ";
    listStaticSuffix[17] = "Seventeen ";
    listStaticSuffix[18] = "Eighteen ";
    listStaticSuffix[19] = "Nineteen ";
    listStaticSuffix[20] = "Twenty ";
    listStaticSuffix[30] = "Thirty ";
    listStaticSuffix[40] = "Fourty ";
    listStaticSuffix[50] = "Fifty ";
    listStaticSuffix[60] = "Sixty ";
    listStaticSuffix[70] = "Seventy ";
    listStaticSuffix[80] = "Eighty ";
    listStaticSuffix[90] = "Ninty ";
};

InrToWordConverter.LoadHelpofNotation = function () {
    listHelpNotation[2] = "=1,000 (3 Trailing Zeros)";
    listHelpNotation[3] = "=1,00,000 (5 Trailing Zeros)";
    listHelpNotation[4] = "=1,00,00,000 (7 Trailing Zeros)";
    listHelpNotation[5] = "=1,00,00,00,000 (9 Trailing Zeros)";
    listHelpNotation[6] = "=1,00,00,00,00,000 (11 Trailing Zeros)";
    listHelpNotation[7] = "=1,00,00,00,00,00,000 (13 Trailing Zeros)";
    listHelpNotation[8] = "=1,00,00,00,00,00,00,000 (15 Trailing Zeros)";
    listHelpNotation[9] = "=1,00,00,00,00,00,00,00,000 (17 Trailing Zeros)";
    listHelpNotation[10] = "=1,00,00,00,00,00,00,00,00,000 (19 Trailing Zeros)";
    listHelpNotation[11] = "=1,00,00,00,00,00,00,00,00,00,000 (21 Trailing Zeros)";
    listHelpNotation[12] = "=1,00,00,00,00,00,00,00,00,00,00,000 (23 Trailing Zeros)";
    listHelpNotation[13] = "=1,00,00,00,00,00,00,00,00,00,00,00,000 (25 Trailing Zeros)";
    listHelpNotation[14] = "=1,00,00,00,00,00,00,00,00,00,00,00,00,000 (27 Trailing Zeros)";
    listHelpNotation[15] = "=1,00,00,00,00,00,00,00,00,00,00,00,00,00,000 (29 Trailing Zeros)";
    listHelpNotation[16] = "=1,00,00,00,00,00,00,00,00,00,00,00,00,00,00,000 (31 Trailing Zeros)";
    listHelpNotation[17] = "=1,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,000 (33 Trailing Zeros)";
    listHelpNotation[18] = "=1,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,000 (35 Trailing Zeros)";
    listHelpNotation[19] = "=1,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,000 (37 Trailing Zeros)";
    listHelpNotation[20] = "=1,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,000 (39 Trailing Zeros)";
};
    if (!String.trim) {
    String.trim = function (str) {
        var result = "";
        var firstNonWhiteSpaceFound = false;
        var startIndex = -1;
        var endIndex = -1;
        if (str) {
            for (var i = 0; i < str.length; i++) {
                if (firstNonWhiteSpaceFound === false) {
                    if (str[i] === ' ' || str[i] === '\t') {
                        continue;
                    }
                    else {
                        firstNonWhiteSpaceFound = true;
                        startIndex = i;
                        endIndex = i;
                    }
                }
                else {
                    if (str[i] === ' ' || str[i] === '\t') {
                        continue;
                    }
                    else {
                        endIndex = i;
                    }
                }
            }
            if (startIndex !== -1 && endIndex !== -1) {
                result = str.slice(startIndex, endIndex + 1);
            }
        }
        return result;
    };
}

Answer 5

Here's a shorter code. with one RegEx and no loops. converts as you wanted, in south asian numbering system

var a = ['','one ','two ','three ','four ', 'five ','six ','seven ','eight ','nine ','ten ','eleven ','twelve ','thirteen ','fourteen ','fifteen ','sixteen ','seventeen ','eighteen ','nineteen '];
var b = ['', '', 'twenty','thirty','forty','fifty', 'sixty','seventy','eighty','ninety'];

function inWords (num) {
    if ((num = num.toString()).length > 9) return 'overflow';
    n = ('000000000' + num).substr(-9).match(/^(\d{2})(\d{2})(\d{2})(\d{1})(\d{2})$/);
    if (!n) return; var str = '';
    str += (n[1] != 0) ? (a[Number(n[1])] || b[n[1][0]] + ' ' + a[n[1][1]]) + 'crore ' : '';
    str += (n[2] != 0) ? (a[Number(n[2])] || b[n[2][0]] + ' ' + a[n[2][1]]) + 'lakh ' : '';
    str += (n[3] != 0) ? (a[Number(n[3])] || b[n[3][0]] + ' ' + a[n[3][1]]) + 'thousand ' : '';
    str += (n[4] != 0) ? (a[Number(n[4])] || b[n[4][0]] + ' ' + a[n[4][1]]) + 'hundred ' : '';
    str += (n[5] != 0) ? ((str != '') ? 'and ' : '') + (a[Number(n[5])] || b[n[5][0]] + ' ' + a[n[5][1]]) + 'only ' : '';
    return str;
}

The only limitation is, you can convert maximum of 9 digits, which I think is more than sufficient in most cases..

Update: Looks like this is more useful than I thought. I've just published this on npm. https://www.npmjs.com/package/num-words

Answer 6

I've just written paisa.js to do this, and it handles lakhs and crores correctly as well, can check it out. The core looks a bit like this:

const regulars = [
  {
    1: 'one', 2: 'two', 3: 'three', 4: 'four', 5: 'five', 6: 'six', 7: 'seven', 8: 'eight', 9: 'nine'
  },
  {
    2: 'twenty', 3: 'thirty', 4: 'forty', 5: 'fifty', 6: 'sixty', 7: 'seventy', 8: 'eighty', 9: 'ninety'
  }
]

const exceptions = {
  10: 'ten',
  11: 'eleven',
  12: 'twelve',
  13: 'thirteen',
  14: 'fourteen',
  15: 'fifteen',
  16: 'sixteen',
  17: 'seventeen',
  18: 'eighteen',
  19: 'nineteen'
}

const partInWords = (part) => {
  if (parseInt(part) === 0) return
  const digits = part.split('')
  const words = []
  if (digits.length === 3) {
    words.push([regulars[0][digits.shift()], 'hundred'].join(' '))
  }
  if (exceptions[digits.join('')]) {
    words.push(exceptions[digits.join('')])
  } else {
    words.push(digits.reverse().reduce((memo, el, i) => {
      memo.unshift(regulars[i][el])
      return memo
    }, []).filter(w => w).join(' '))
  }
  return words.filter(w => w.trim().length).join(' and ')
}