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

My Tactic goes like this:

• Separate the digits to three and put them on Array (finlOutPut), from right to left.

• Convert each group (each cell in the finlOutPut array) of three digits to a word (this what the triConvert function does). If all the three digits are zero convert them to "dontAddBigSuffix"

• From Right to left, add thousand, million, billion, etc. If the finlOutPut cell equals "dontAddBigSufix" (because it was only zeroes), don't add the word and set the cell to " " (nothing).

It seems to work pretty well, but I've got some problems with numbers like 190000009, converted to: "one hundred ninety million". Somehow it "forgets" the last numbers when there are a few zeros.

What did I do wrong? Where is the bug? Why does it not work perfectly?

function update(){
    var bigNumArry = new Array('', ' thousand', ' million', ' billion', ' trillion', ' quadrillion', ' quintillion');

    var output = '';
    var numString =   document.getElementById('number').value;
    var finlOutPut = new Array();

    if (numString == '0') {
        document.getElementById('container').innerHTML = 'Zero';
        return;
    }

    if (numString == 0) {
        document.getElementById('container').innerHTML = 'messeg tell to enter numbers';
        return;
    }

    var i = numString.length;
    i = i - 1;

    //cut the number to grups of three digits and add them to the Arry
    while (numString.length > 3) {
        var triDig = new Array(3);
        triDig[2] = numString.charAt(numString.length - 1);
        triDig[1] = numString.charAt(numString.length - 2);
        triDig[0] = numString.charAt(numString.length - 3);

        var varToAdd = triDig[0] + triDig[1] + triDig[2];
        finlOutPut.push(varToAdd);
        i--;
        numString = numString.substring(0, numString.length - 3);
    }
    finlOutPut.push(numString);
    finlOutPut.reverse();

    //conver each grup of three digits to english word
    //if all digits are zero the triConvert
    //function return the string "dontAddBigSufix"
    for (j = 0; j < finlOutPut.length; j++) {
        finlOutPut[j] = triConvert(parseInt(finlOutPut[j]));
    }

    var bigScalCntr = 0; //this int mark the million billion trillion... Arry

    for (b = finlOutPut.length - 1; b >= 0; b--) {
        if (finlOutPut[b] != "dontAddBigSufix") {
            finlOutPut[b] = finlOutPut[b] + bigNumArry[bigScalCntr] + ' , ';
            bigScalCntr++;
        }
        else {
            //replace the string at finlOP[b] from "dontAddBigSufix" to empty String.
            finlOutPut[b] = ' ';
            bigScalCntr++; //advance the counter  
        }
    }

        //convert The output Arry to , more printable string 
        for(n = 0; n<finlOutPut.length; n++){
            output +=finlOutPut[n];
        }

    document.getElementById('container').innerHTML = output;//print the output
}

//simple function to convert from numbers to words from 1 to 999
function triConvert(num){
    var ones = new Array('', ' one', ' two', ' three', ' four', ' five', ' six', ' seven', ' eight', ' nine', ' ten', ' eleven', ' twelve', ' thirteen', ' fourteen', ' fifteen', ' sixteen', ' seventeen', ' eighteen', ' nineteen');
    var tens = new Array('', '', ' twenty', ' thirty', ' forty', ' fifty', ' sixty', ' seventy', ' eighty', ' ninety');
    var hundred = ' hundred';
    var output = '';
    var numString = num.toString();

    if (num == 0) {
        return 'dontAddBigSufix';
    }
    //the case of 10, 11, 12 ,13, .... 19 
    if (num < 20) {
        output = ones[num];
        return output;
    }

    //100 and more
    if (numString.length == 3) {
        output = ones[parseInt(numString.charAt(0))] + hundred;
        output += tens[parseInt(numString.charAt(1))];
        output += ones[parseInt(numString.charAt(2))];
        return output;
    }

    output += tens[parseInt(numString.charAt(0))];
    output += ones[parseInt(numString.charAt(1))];

    return output;
}   

<input type="text"
    id="number"
    size="70"
    onkeyup="update();"
    /*this code prevent non numeric letters*/ 
    onkeydown="return (event.ctrlKey || event.altKey 
                    || (47<event.keyCode && event.keyCode<58 && event.shiftKey==false) 
                    || (95<event.keyCode &a开发者_StackOverflowmp;& event.keyCode<106)
                    || (event.keyCode==8) || (event.keyCode==9) 
                    || (event.keyCode>34 && event.keyCode<40) 
                    || (event.keyCode==46) )"/>
                    <br/>
<div id="container">Here The Numbers Printed</div>

---

JavaScript is parsing the group of 3 numbers as an octal number when there's a leading zero digit. When the group of three digits is all zeros, the result is the same whether the base is octal or decimal.

But when you give JavaScript '009' (or '008'), that's an invalid octal number, so you get zero back.

If you had gone through the whole set of numbers from 190,000,001 to 190,000,010 you'd hav seen JavaScript skip '...,008' and '...,009' but emit 'eight' for '...,010'. That's the 'Eureka!' moment.

Change:

for (j = 0; j < finlOutPut.length; j++) {
    finlOutPut[j] = triConvert(parseInt(finlOutPut[j]));
}

to

for (j = 0; j < finlOutPut.length; j++) {
    finlOutPut[j] = triConvert(parseInt(finlOutPut[j],10));
}

Code also kept on adding commas after every non-zero group, so I played with it and found the right spot to add the comma.

Old:

for (b = finlOutPut.length - 1; b >= 0; b--) {
    if (finlOutPut[b] != "dontAddBigSufix") {
        finlOutPut[b] = finlOutPut[b] + bigNumArry[bigScalCntr] + ' , ';
        bigScalCntr++;
    }
    else {
        //replace the string at finlOP[b] from "dontAddBigSufix" to empty String.
        finlOutPut[b] = ' ';
        bigScalCntr++; //advance the counter  
    }
}

    //convert The output Arry to , more printable string 
    for(n = 0; n<finlOutPut.length; n++){
        output +=finlOutPut[n];
    }

New:

for (b = finlOutPut.length - 1; b >= 0; b--) {
    if (finlOutPut[b] != "dontAddBigSufix") {
        finlOutPut[b] = finlOutPut[b] + bigNumArry[bigScalCntr]; // <<<
        bigScalCntr++;
    }
    else {
        //replace the string at finlOP[b] from "dontAddBigSufix" to empty String.
        finlOutPut[b] = ' ';
        bigScalCntr++; //advance the counter  
    }
}

    //convert The output Arry to , more printable string 
    var nonzero = false; // <<<
    for(n = 0; n<finlOutPut.length; n++){
        if (finlOutPut[n] != ' ') { // <<<
            if (nonzero) output += ' , '; // <<<
            nonzero = true; // <<<
        } // <<<
        output +=finlOutPut[n];
    }

---

Your problem is already solved but I am posting another way of doing it just for reference.

The code was written to be tested on node.js, but the functions should work fine when called within the browser. Also, this only handles the range [0,1000000], but can be easily adapted for bigger ranges.

// actual  conversion code starts here

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

function convert_millions(num) {
  if (num >= 1000000) {
    return convert_millions(Math.floor(num / 1000000)) + " million " + convert_thousands(num % 1000000);
  } else {
    return convert_thousands(num);
  }
}

function convert_thousands(num) {
  if (num >= 1000) {
    return convert_hundreds(Math.floor(num / 1000)) + " thousand " + convert_hundreds(num % 1000);
  } else {
    return convert_hundreds(num);
  }
}

function convert_hundreds(num) {
  if (num > 99) {
    return ones[Math.floor(num / 100)] + " hundred " + convert_tens(num % 100);
  } else {
    return convert_tens(num);
  }
}

function convert_tens(num) {
  if (num < 10) return ones[num];
  else if (num >= 10 && num < 20) return teens[num - 10];
  else {
    return tens[Math.floor(num / 10)] + " " + ones[num % 10];
  }
}

function convert(num) {
  if (num == 0) return "zero";
  else return convert_millions(num);
}

//end of conversion code

//testing code begins here

function main() {
  var cases = [0, 1, 2, 7, 10, 11, 12, 13, 15, 19, 20, 21, 25, 29, 30, 35, 50, 55, 69, 70, 99, 100, 101, 119, 510, 900, 1000, 5001, 5019, 5555, 10000, 11000, 100000, 199001, 1000000, 1111111, 190000009];
  for (var i = 0; i < cases.length; i++) {
    console.log(cases[i] + ": " + convert(cases[i]));
  }
}

main();

---

I know this problem had solved 3 years ago. I am posting this SPECIALLY FOR INDIAN DEVELOPERS

After spending some time in googling and playing with others code i made a quick fix and reusable function works well for numbers upto 99,99,99,999. use : number2text(1234.56); will return ONE THOUSAND TWO HUNDRED AND THIRTY-FOUR RUPEE AND FIFTY-SIX PAISE ONLY . enjoy !

function number2text(value) {
    var fraction = Math.round(frac(value)*100);
    var f_text  = "";

    if(fraction > 0) {
        f_text = "AND "+convert_number(fraction)+" PAISE";
    }

    return convert_number(value)+" RUPEE "+f_text+" ONLY";
}

function frac(f) {
    return f % 1;
}

function convert_number(number)
{
    if ((number < 0) || (number > 999999999)) 
    { 
        return "NUMBER OUT OF RANGE!";
    }
    var Gn = Math.floor(number / 10000000);  /* Crore */ 
    number -= Gn * 10000000; 
    var kn = Math.floor(number / 100000);     /* lakhs */ 
    number -= kn * 100000; 
    var Hn = Math.floor(number / 1000);      /* thousand */ 
    number -= Hn * 1000; 
    var Dn = Math.floor(number / 100);       /* Tens (deca) */ 
    number = number % 100;               /* Ones */ 
    var tn= Math.floor(number / 10); 
    var one=Math.floor(number % 10); 
    var res = ""; 

    if (Gn>0) 
    { 
        res += (convert_number(Gn) + " CRORE"); 
    } 
    if (kn>0) 
    { 
            res += (((res=="") ? "" : " ") + 
            convert_number(kn) + " LAKH"); 
    } 
    if (Hn>0) 
    { 
        res += (((res=="") ? "" : " ") +
            convert_number(Hn) + " THOUSAND"); 
    } 

    if (Dn) 
    { 
        res += (((res=="") ? "" : " ") + 
            convert_number(Dn) + " HUNDRED"); 
    } 


    var ones = Array("", "ONE", "TWO", "THREE", "FOUR", "FIVE", "SIX","SEVEN", "EIGHT", "NINE", "TEN", "ELEVEN", "TWELVE", "THIRTEEN","FOURTEEN", "FIFTEEN", "SIXTEEN", "SEVENTEEN", "EIGHTEEN","NINETEEN"); 
var tens = Array("", "", "TWENTY", "THIRTY", "FOURTY", "FIFTY", "SIXTY","SEVENTY", "EIGHTY", "NINETY"); 

    if (tn>0 || one>0) 
    { 
        if (!(res=="")) 
        { 
            res += " AND "; 
        } 
        if (tn < 2) 
        { 
            res += ones[tn * 10 + one]; 
        } 
        else 
        { 

            res += tens[tn];
            if (one>0) 
            { 
                res += ("-" + ones[one]); 
            } 
        } 
    }

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

---

Indian Version

Updated version of @jasonhao 's answer for Indian currency

function intToEnglish(number) {

  var NS = [
    { value: 10000000, str: "Crore" },
    { value: 100000, str: "Lakh" },
    { value: 1000, str: "Thousand" },
    { value: 100, str: "Hundred" },
    { value: 90, str: "Ninety" },
    { value: 80, str: "Eighty" },
    { value: 70, str: "Seventy" },
    { value: 60, str: "Sixty" },
    { value: 50, str: "Fifty" },
    { value: 40, str: "Forty" },
    { value: 30, str: "Thirty" },
    { value: 20, str: "Twenty" },
    { value: 19, str: "Nineteen" },
    { value: 18, str: "Eighteen" },
    { value: 17, str: "Seventeen" },
    { value: 16, str: "Sixteen" },
    { value: 15, str: "Fifteen" },
    { value: 14, str: "Fourteen" },
    { value: 13, str: "Thirteen" },
    { value: 12, str: "Twelve" },
    { value: 11, str: "Eleven" },
    { value: 10, str: "Ten" },
    { value: 9, str: "Nine" },
    { value: 8, str: "Eight" },
    { value: 7, str: "Seven" },
    { value: 6, str: "Six" },
    { value: 5, str: "Five" },
    { value: 4, str: "Four" },
    { value: 3, str: "Three" },
    { value: 2, str: "Two" },
    { value: 1, str: "One" }
  ];

  var result = '';
  for (var n of NS) {
    if (number >= n.value) {
      if (number <= 99) {
        result += n.str;
        number -= n.value;
        if (number > 0) result += ' ';
      } else {
        var t = Math.floor(number / n.value);
        // console.log(t);
        var d = number % n.value;
        if (d > 0) {
          return intToEnglish(t) + ' ' + n.str + ' ' + intToEnglish(d);
        } else {
          return intToEnglish(t) + ' ' + n.str;
        }

      }
    }
  }
  return result;
}

console.log(intToEnglish(99))
console.log(intToEnglish(991199))
console.log(intToEnglish(123456799))

---

There are JS library for en_US and cs_CZ.
You can use it standalone or as Node module.

• Numbers2Words

---

Here, I wrote an alternative solution:

1) The object containing the string constants:

var NUMBER2TEXT = {
    ones: ['', 'one', 'two', 'three', 'four', 'five', 'six', 'seven', 'eight', 'nine', 'ten', 'eleven', 'twelve', 'thirteen', 'fourteen', 'fifteen', 'sixteen', 'seventeen', 'eighteen', 'nineteen'],
    tens: ['', '', 'twenty', 'thirty', 'fourty', 'fifty', 'sixty', 'seventy', 'eighty', 'ninety'],
    sep: ['', ' thousand ', ' million ', ' billion ', ' trillion ', ' quadrillion ', ' quintillion ', ' sextillion ']
};

2) The actual code:

(function( ones, tens, sep ) {

    var input = document.getElementById( 'input' ),
        output = document.getElementById( 'output' );

    input.onkeyup = function() {
        var val = this.value,
            arr = [],
            str = '',
            i = 0;

        if ( val.length === 0 ) {
            output.textContent = 'Please type a number into the text-box.';
            return;  
        }

        val = parseInt( val, 10 );
        if ( isNaN( val ) ) {
            output.textContent = 'Invalid input.';
            return;   
        }

        while ( val ) {
            arr.push( val % 1000 );
            val = parseInt( val / 1000, 10 );   
        }

        while ( arr.length ) {
            str = (function( a ) {
                var x = Math.floor( a / 100 ),
                    y = Math.floor( a / 10 ) % 10,
                    z = a % 10;

                return ( x > 0 ? ones[x] + ' hundred ' : '' ) +
                       ( y >= 2 ? tens[y] + ' ' + ones[z] : ones[10*y + z] );
            })( arr.shift() ) + sep[i++] + str;
        }

        output.textContent = str;
    };

})( NUMBER2TEXT.ones, NUMBER2TEXT.tens, NUMBER2TEXT.sep );

Live demo: http://jsfiddle.net/j5kdG/

---

A version with a compact object - for numbers from zero to 999.

function wordify(n) {
    var word = [],
        numbers = { 1: 'One', 2: 'Two', 3: 'Three', 4: 'Four', 5: 'Five', 6: 'Six', 7: 'Seven', 8: 'Eight', 9: 'Nine', 10: 'Ten', 11: 'Eleven', 12: 'Twelve', t3: 'Thir', t5: 'Fif', t8: 'Eigh', 20: 'Twenty' },
        hundreds = 0 | (n % 1000) / 100,
        tens = 0 | (n % 100) / 10,
        ones = n % 10,
        part;

    if (n === 0) return 'Zero';
    if (hundreds) word.push(numbers[hundreds] + ' Hundred');

    if (tens === 0) {
        word.push(numbers[ones]);
    } else if (tens === 1) {
        word.push(numbers['1' + ones] || (numbers['t' + ones] || numbers[ones]) + 'teen');
    } else {
        part = numbers[tens + '0'] || (numbers['t' + tens] || numbers[tens]) + 'ty';
        word.push(numbers[ones] ? part + '-' + numbers[ones] : part);
    }
    return word.join(' ');
}

var i,
    output = document.getElementById('out');

for (i = 0; i < 1e3; i++) output.innerHTML += wordify(i) + '\n';

<pre id="out"></pre>

---

<html>
<head>
<meta http-equiv="Content-Type" content="text/html;charset=utf-8"/>
<script type="text/javascript">
var th = ['', ' thousand', ' million', ' billion', ' trillion', ' quadrillion', ' quintillion'];
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 update(){
    var numString =   document.getElementById('number').value;
    if (numString == '0') {
        document.getElementById('container').innerHTML = 'Zero';
        return;
    }
    if (numString == 0) {
        document.getElementById('container').innerHTML = 'messeg tell to enter numbers';
        return;
    }

    var output = toWords(numString);
    //print the output
    document.getElementById('container').innerHTML = output;
}

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) {
            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, ' ');
}
</script>

</head>
<body>

<input type="text"
    id="number"
    size="70"
    onkeyup="update();"
    /*this code prevent non numeric letters*/ 
    onkeydown="return (event.ctrlKey || event.altKey 
                    || (47<event.keyCode && event.keyCode<58 && event.shiftKey==false) 
                    || (95<event.keyCode && event.keyCode<106)
                    || (event.keyCode==8) || (event.keyCode==9) 
                    || (event.keyCode>34 && event.keyCode<40) 
                    || (event.keyCode==46) )"/>
                    <br/>
<div id="container">Here The Numbers Printed</div>
</body>
</html>

---

Try this,convert number to words

function convert(number) {

    if (number < 0) {

        console.log("Number Must be greater than zero = " + number);
        return "";
    }
    if (number > 100000000000000000000) {
        console.log("Number is out of range = " + number);
        return "";
    }
    if (!is_numeric(number)) {
        console.log("Not a number = " + number);
        return "";
    }

    var quintillion = Math.floor(number / 1000000000000000000); /* quintillion */
    number -= quintillion * 1000000000000000000;
    var quar = Math.floor(number / 1000000000000000); /* quadrillion */
    number -= quar * 1000000000000000;
    var trin = Math.floor(number / 1000000000000); /* trillion */
    number -= trin * 1000000000000;
    var Gn = Math.floor(number / 1000000000); /* billion */
    number -= Gn * 1000000000;
    var million = Math.floor(number / 1000000); /* million */
    number -= million * 1000000;
    var Hn = Math.floor(number / 1000); /* thousand */
    number -= Hn * 1000;
    var Dn = Math.floor(number / 100); /* Tens (deca) */
    number = number % 100; /* Ones */
    var tn = Math.floor(number / 10);
    var one = Math.floor(number % 10);
    var res = "";

    if (quintillion > 0) {
        res += (convert_number(quintillion) + " quintillion");
    }
    if (quar > 0) {
        res += (convert_number(quar) + " quadrillion");
    }
    if (trin > 0) {
        res += (convert_number(trin) + " trillion");
    }
    if (Gn > 0) {
        res += (convert_number(Gn) + " billion");
    }
    if (million > 0) {
        res += (((res == "") ? "" : " ") + convert_number(million) + " million");
    }
    if (Hn > 0) {
        res += (((res == "") ? "" : " ") + convert_number(Hn) + " Thousand");
    }

    if (Dn) {
        res += (((res == "") ? "" : " ") + convert_number(Dn) + " hundred");
    }


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

    if (tn > 0 || one > 0) {
        if (!(res == "")) {
            res += " and ";
        }
        if (tn < 2) {
            res += ones[tn * 10 + one];
        } else {

            res += tens[tn];
            if (one > 0) {
                res += ("-" + ones[one]);
            }
        }
    }

    if (res == "") {
        console.log("Empty = " + number);
        res = "";
    }
    return res;
}
function is_numeric(mixed_var) {
    return (typeof mixed_var === 'number' || typeof mixed_var === 'string') && mixed_var !== '' && !isNaN(mixed_var);
}

---

function intToEnglish(number){

var NS = [
    {value: 1000000000000000000000, str: "sextillion"},
    {value: 1000000000000000000, str: "quintillion"},
    {value: 1000000000000000, str: "quadrillion"},
    {value: 1000000000000, str: "trillion"},
    {value: 1000000000, str: "billion"},
    {value: 1000000, str: "million"},
    {value: 1000, str: "thousand"},
    {value: 100, str: "hundred"},
    {value: 90, str: "ninety"},
    {value: 80, str: "eighty"},
    {value: 70, str: "seventy"},
    {value: 60, str: "sixty"},
    {value: 50, str: "fifty"},
    {value: 40, str: "forty"},
    {value: 30, str: "thirty"},
    {value: 20, str: "twenty"},
    {value: 19, str: "nineteen"},
    {value: 18, str: "eighteen"},
    {value: 17, str: "seventeen"},
    {value: 16, str: "sixteen"},
    {value: 15, str: "fifteen"},
    {value: 14, str: "fourteen"},
    {value: 13, str: "thirteen"},
    {value: 12, str: "twelve"},
    {value: 11, str: "eleven"},
    {value: 10, str: "ten"},
    {value: 9, str: "nine"},
    {value: 8, str: "eight"},
    {value: 7, str: "seven"},
    {value: 6, str: "six"},
    {value: 5, str: "five"},
    {value: 4, str: "four"},
    {value: 3, str: "three"},
    {value: 2, str: "two"},
    {value: 1, str: "one"}
  ];

  var result = '';
  for (var n of NS) {
    if(number>=n.value){
      if(number<=20){
        result += n.str;
        number -= n.value;
        if(number>0) result += ' ';
      }else{
        var t =  Math.floor(number / n.value);
        var d = number % n.value;
        if(d>0){
          return intToEnglish(t) + ' ' + n.str +' ' + intToEnglish(d);
        }else{
          return intToEnglish(t) + ' ' + n.str;
        }

      }
    }
  }
  return result;
}

---

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)
}

---

Here's a solution that will handle any integer value that fit's in a string. I've defined number scales up to "decillion", so this solution should be accurate up to 999 decillion. After which you get things like "one thousand decillion" and so on.

JavaScript numbers start to fail around "999999999999999" so the convert function works with strings of numbers only.

Examples:

convert("365");
//=> "three hundred sixty-five"

convert("10000000000000000000000000000230001010109");
//=> "ten thousand decillion two hundred thirty billion one million ten thousand one hundred nine"

Code:

var lt20 = ["", "one", "two", "three", "four", "five", "six", "seven","eight", "nine", "ten", "eleven", "twelve", "thirteen", "fourteen", "fifteen", "sixteen", "seventeen", "eighteen", "nineteen" ],
    tens = ["", "ten", "twenty", "thirty", "fourty", "fifty", "sixty", "seventy", "eightty", "ninety" ],
    scales = ["", "thousand", "million", "billion", "trillion", "quadrillion", "quintillion", "sextillion", "septillion", "octillion", "nonillion", "decillion" ],
    max = scales.length * 3;

function convert(val) {
    var len;

    // special cases
    if (val[0] === "-") { return "negative " + convert(val.slice(1)); }
    if (val === "0") { return "zero"; }

    val = trim_zeros(val);
    len = val.length;

    // general cases
    if (len < max) { return convert_lt_max(val); }
    if (len >= max) { return convert_max(val); }
}

function convert_max(val) {
    return split_rl(val, max)
        .map(function (val, i, arr) {
            if (i < arr.length - 1) {
                return convert_lt_max(val) + " " + scales.slice(-1);
            }
            return convert_lt_max(val);
        })
        .join(" ");
}       

function convert_lt_max(val) {
    var l = val.length;
    if (l < 4) {
        return convert_lt1000(val).trim();
    } else {
        return split_rl(val, 3)
            .map(convert_lt1000)
            .reverse()
            .map(with_scale)
            .reverse()
            .join(" ")
            .trim();
    }
}

function convert_lt1000(val) {
    var rem, l;

    val = trim_zeros(val);
    l = val.length;

    if (l === 0) { return ""; }
    if (l < 3) { return convert_lt100(val); }
    if (l === 3) { //less than 1000
        rem = val.slice(1);
        if (rem) {
            return lt20[val[0]] + " hundred " + convert_lt1000(rem);
        } else {
            return lt20[val[0]] + " hundred";
        }
    }
}

function convert_lt100(val) {
    if (is_lt20(val)) { // less than 20
        return lt20[val];
    } else if (val[1] === "0") {
        return tens[val[0]];
    } else {
        return tens[val[0]] + "-" +  lt20[val[1]];
    }
}


function split_rl(str, n) {
    // takes a string 'str' and an integer 'n'. Splits 'str' into
    // groups of 'n' chars and returns the result as an array. Works
    // from right to left.
    if (str) {
        return Array.prototype.concat
            .apply(split_rl(str.slice(0, (-n)), n), [str.slice(-n)]);
    } else {
        return [];
    }
}

function with_scale(str, i) {
    var scale;
    if (str && i > (-1)) {
        scale = scales[i];
        if (scale !== undefined) {
            return str.trim() + " " + scale;
        } else {
            return convert(str.trim());
        }
    } else {
        return "";
    }
}

function trim_zeros(val) {
    return val.replace(/^0*/, "");
}

function is_lt20(val) {
    return parseInt(val, 10) < 20;
}

---

I've modified the posting from Šime Vidas - http://jsfiddle.net/j5kdG/ To include dollars, cents, commas and "and" in the appropriate places. There's an optional ending if it requires "zero cents" or no mention of cents if 0.

This function structure did my head in a bit but I learned heaps. Thanks Sime.

Someone might find a better way of processing this.

Code:

var str='';
var str2='';
var str3 =[];

function convertNum(inp,end){
    str2='';
    str3 = [];
    var NUMBER2TEXT = {
    ones: ['', 'one', 'two', 'three', 'four', 'five', 'six', 'seven', 'eight', 'nine', 'ten', 'eleven', 'twelve', 'thirteen', 'fourteen', 'fifteen', 'sixteen', 'seventeen', 'eighteen', 'nineteen'],
    tens: ['', '', 'twenty', 'thirty', 'forty', 'fifty', 'sixty', 'seventy', 'eighty', 'ninety'],
    sep: ['', ' thousand', ' million', ' billion', ' trillion', ' quadrillion', ' quintillion', ' sextillion']
};
(function( ones, tens, sep ) {
   var vals = inp.split("."),val,pos,postsep=' ';
   for (p in vals){
      val = vals[p], arr = [], str = '', i = 0;
      if ( val.length === 0 ) {return 'No value';}
      val = parseInt( (p==1 && val.length===1 )?val*10:val, 10 );
      if ( isNaN( val ) || p>=2) {return 'Invalid value'; }
      while ( val ) {
        arr.push( val % 1000 );
        val = parseInt( val / 1000, 10 );   
      }
      pos = arr.length;
      function trimx (strx) {
                return strx.replace(/^\s\s*/, '').replace(/\s\s*$/, '');
            }
        function seps(sepi,i){
                var s = str3.length
                if (str3[s-1][0]){
                    if (str3[s-2][1] === str3[s-1][0]){
                        str = str.replace(str3[s-2][1],'')
                    }
                }
                var temp = str.split(sep[i-2]);
                if (temp.length > 1){
                    if (trimx(temp[0]) ==='' && temp[1].length > 1 ){
                        str = temp[1];
                        } 
                    }
                return sepi + str ;
        }
      while ( arr.length  ) {
        str = (function( a ) {
            var x = Math.floor( a / 100 ),
                y = Math.floor( a / 10 ) % 10,
                z = a % 10;
                postsep = (arr.length != 0)?', ' : ' ' ;
                if ((x+y+z) === 0){
                    postsep = ' '
                }else{ 
                    if (arr.length == pos-1 && x===0 && pos > 1 ){
                        postsep = ' and ' 
                    } 
                }
               str3.push([trimx(str)+"",trimx(sep[i])+""]);
                return  (postsep)+( x > 0 ? ones[x] + ' hundred ' + (( x == 0 && y >= 0 || z >0 )?' and ':' ') : ' ' ) +                  
                   ( y >= 2 ? tens[y] + ((z===0)?' ':'-') + ones[z] : ones[10*y + z] ); 
        })( arr.shift() ) +seps( sep[i++] ,i ) ;             
      }
      if (p==0){ str2 += str + ' dollars'}
      if (p==1 && !end){str2 += (str!='')?' and '+ str + ' cents':'' } 
      if (p==1 && end ){str2 += ' and ' + ((str==='')?'zero':str) + ' cents '} 
   }
})( NUMBER2TEXT.ones , NUMBER2TEXT.tens , NUMBER2TEXT.sep );

---

this is the solution for french language it's a fork for @gandil response

<html>
<head>
<meta http-equiv="Content-Type" content="text/html;charset=utf-8"/>
<script type="text/javascript">
var th = ['', ' mille', ' millions', ' milliards', ' billions', ' mille-billions', ' trillion'];
var dg = ['zéro', 'un', 'deux', 'trois', 'quatre', 'cinq', 'six', 'sept', 'huit', 'neuf'];
var tn = ['dix', 'onze', 'douze', 'treize', 'quatorze', 'quinze', 'seize', 'dix-sept', 'dix-huit', 'dix-neuf'];
var tw = ['vingt', 'trente', 'quarante', 'cinquante', 'soixante', 'soixante-dix', 'quatre-vingts', 'quatre-vingt-dix'];

function update(){
    var numString =   document.getElementById('number').value;
    if (numString == '0') {
        document.getElementById('container').innerHTML = 'Zéro';
        return;
    }
    if (numString == 0) {
        document.getElementById('container').innerHTML = 'messeg tell to enter numbers';
        return;
    }

    var output = toWords(numString);
    //output.split('un mille').join('msille ');
    //output.replace('un cent', 'cent ');
    //print the output
    //if(output.length == 4){output = 'sss';}
    document.getElementById('container').innerHTML = output;
}

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) {
            str += dg[n[i]] + ' ';
            //if((dg[n[i]] == 'un') && ((x - i) / 3 == 1)){str = 'cent ';}
            if ((x - i) % 3 == 0) {str += 'cent ';}
            sk = 1;
        }
        if ((x - i) % 3 == 1) {
            //test
            if((x - i - 1) / 3 == 1){
                var long = str.length;
                subs = str.substr(long-3);
                if(subs.search("un")!= -1){
                    //str += 'OK';
                    str = str.substr(0, long-4);
                }

            }




            //test
            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]] + ' ';
    }
    //if(str.length == 4){}
    str.replace(/\s+/g, ' ');
    return str.split('un cent').join('cent ');
    //return str.replace('un cent', 'cent ');
}
</script>

</head>
<body>

<input type="text"
       id="number"
       size="70"
       onkeyup="update();"
/*this code prevent non numeric letters*/
onkeydown="return (event.ctrlKey || event.altKey
|| (47<event.keyCode && event.keyCode<58 && event.shiftKey==false)
|| (95<event.keyCode && event.keyCode<106)
|| (event.keyCode==8) || (event.keyCode==9)
|| (event.keyCode>34 && event.keyCode<40)
|| (event.keyCode==46) )"/>
<br/>
<div id="container">Here The Numbers Printed</div>
</body>
</html>

i hope it will help

---

A little code snippet for INDONESIAN DEVELOPER to translate numeric value into verbal spelling (minimized by hand, only 576 bytes, requires ES6+)...

const terbilang=(x,nol='---',min='minus')=>{const S=['','satu','dua','tiga','empat','lima','enam','tujuh','delapan','sembilan'],K=['','ribu','juta','miliar','triliun','kuadriliun'],s=[];if(!x)return nol;if(x<0){if(min)s=[min];x=-x}for(let k=0;x;k++){let g=x%1e3;if(g===1&&k===1)s.unshift('seribu');else{let u=g>99?[(g>199?S[g/100|0]+' ':'se')+'ratus']:[];if(g%=100){if(g>9&&g<20)u.push(g<11?'sepuluh':(g<12?'se':S[g%10]+' ')+'belas');else{if(g>19)u.push(S[g/10|0]+' puluh');if(g%=10)u.push(S[g])}}k&&u.push(K[k]);s.unshift(u.join(' '))}x=Math.floor(x/1e3)}return s.join(' ')};

---

function toWords(...x) {
    let space = /\s/g;
    let digit = /\d/g;
    let trio = /.../g;
    let unit = ' one two three four five six seven eight nine ten eleven twelve thirteen fourteen fifteen sixteen seventeen eighteen nineteen'.split(space);
    let ten = '  twenty thirty forty fifty sixty seventy eighty ninety'.split(space);
    let scale = ' thousand million billion trillion quadrillion quintillion sextillion septillion octillion nonillion decillion'.split(space);
    let d = digit.test(x) ? String(x).match(digit) : ['0'];
    while (d.length % 3) d.unshift('0');
    d = d.join('').match(trio).map(function verbose(string) {
        let number = Number(string);
        return (number < 20) ?
            unit[number] :
            (number < 100) ?
            [ten[Number(string.slice(0, -1))], verbose(string.slice(-1))].filter(Boolean).join('-') :
            [verbose(string.slice(0, -2)), 'hundred', verbose(string.slice(-2))].filter(Boolean).join(' ');
    }).reverse().map(function(v, i, a) {
        return v ? [v, scale[i]].filter(Boolean).join(' ') : v;
    }).reverse().filter(Boolean).join(', ');
    return d ? d : 'zero';
}
toWords('14,702,000,583,690,010');
// 'fourteen quadrillion, seven hundred two trillion, five hundred eighty-three million, six hundred ninety thousand, ten'

---

Update Feb 2022

A simple and short Javascript function to do the conversion of numbers (integers) to words in English (US System) and give the correct results is included below using a forEach() loop with the String Triplets Array method.

The number is first converted into a string triplet array using:

num= ("0".repeat(2*(num+="").length%3)+num).match(/.{3}/g);

The string array is then easily decoded into numbers.

For example, the number 1234567 is converted into an array of string triplets:

[ '001', '234', '567' ]

Each element is then scanned from left to right by the forEach() loop.

This is a far better solution than using a for loop that I had proposed 2 years ago.

You can increase the scale array above the 'Quadrillion' if you prefer.

If the input number is too large, then pass it as a "string".

Test cases are also included.

/********************************************************
* @function    : numToWords(number)
* @purpose     : Converts Unsigned Integers to Words
* @version     : 1.50
* @author      : Mohsen Alyafei
* @licence     : MIT
* @date        : 26 Feb 2022
* @param       : {number} [integer numeric or string]
* @returns     : {string} The wordified number string
********************************************************/


//==============================================================
function numToWords(num = 0) {
if (num == 0) return "Zero";
num= ("0".repeat(2*(num+="").length%3)+num).match(/.{3}/g);
let out="",
    T10s=["","One","Two","Three","Four","Five","Six","Seven","Eight","Nine","Ten","Eleven","Twelve","Thirteen","Fourteen","Fifteen","Sixteen","Seventeen","Eighteen","Nineteen"],
    T20s=["","","Twenty","Thirty","Forty","Fifty","Sixty","Seventy","Eighty","Ninety"],
    sclT=["","Thousand","Million","Billion","Trillion","Quadrillion"];
return num.forEach((n,i) => {
if (+n) {
 let hund=+n[0], ten=+n.substring(1), scl=sclT[num.length-i-1];
 out+=(out?" ":"")+(hund?T10s[hund]+" Hundred":"")+(hund && ten?" ":"")+(ten<20?T10s[ten]:T20s[+n[1]]+(+n[2]?"-":"")+T10s[+n[2]]);
 out+=(out && scl?" ":"")+scl;
}}),out;
}
//==============================================================









//=========================================
//             Test Code
//=========================================
var r=0; // test tracker
r |= test(0,"Zero");
r |= test(5,"Five");
r |= test(10,"Ten");
r |= test(19,"Nineteen");
r |= test(33,"Thirty-Three");
r |= test(100,"One Hundred");
r |= test(111,"One Hundred Eleven");
r |= test(890,"Eight Hundred Ninety");
r |= test(1234,"One Thousand Two Hundred Thirty-Four");
r |= test(12345,"Twelve Thousand Three Hundred Forty-Five");
r |= test(123456,"One Hundred Twenty-Three Thousand Four Hundred Fifty-Six");
r |= test(1234567,"One Million Two Hundred Thirty-Four Thousand Five Hundred Sixty-Seven");
r |= test(12345678,"Twelve Million Three Hundred Forty-Five Thousand Six Hundred Seventy-Eight");
r |= test(123456789,"One Hundred Twenty-Three Million Four Hundred Fifty-Six Thousand Seven Hundred Eighty-Nine");
r |= test(1234567890,"One Billion Two Hundred Thirty-Four Million Five Hundred Sixty-Seven Thousand Eight Hundred Ninety");
r |= test(1001,"One Thousand One");
r |= test(10001,"Ten Thousand One");
r |= test(100001,"One Hundred Thousand One");
r |= test(1000001,"One Million One");
r |= test(10000001,"Ten Million One");
r |= test(100000001,"One Hundred Million One");
r |= test(12012,"Twelve Thousand Twelve");
r |= test(120012,"One Hundred Twenty Thousand Twelve");
r |= test(1200012,"One Million Two Hundred Thousand Twelve");
r |= test(12000012,"Twelve Million Twelve");
r |= test(120000012,"One Hundred Twenty Million Twelve");
r |= test(75075,"Seventy-Five Thousand Seventy-Five");
r |= test(750075,"Seven Hundred Fifty Thousand Seventy-Five");
r |= test(7500075,"Seven Million Five Hundred Thousand Seventy-Five");
r |= test(75000075,"Seventy-Five Million Seventy-Five");
r |= test(750000075,"Seven Hundred Fifty Million Seventy-Five");
r |= test(1000,"One Thousand");
r |= test(1000000,"One Million");
r |= test(1000000000,"One Billion");
r |= test(1000000000000,"One Trillion");
r |= test("1000000000000000","One Quadrillion");

if (r==0) console.log("All Test Cases Passed.");

function test(n,should) {
let result = numToWords(n);
if (result !== should) {console.log(`${n} Output   : ${result}\n${n} Should be: ${should}`);return 1;}
}

---

I would like to point out that the original logic fails for values between x11-x19, where x >= 1. For example, 118 returns "one hundred eight". This is because these numbers are processed by the following code in triConvert():

//100 and more
if (numString.length == 3) {
    output = ones[parseInt(numString.charAt(0))] + hundred;
    output += tens[parseInt(numString.charAt(1))];
    output += ones[parseInt(numString.charAt(2))];
    return output;
}

here, the character representing the tens digit is used to index the tens[] array, which has an empty string at index [1], so 118 become 108 in effect.

It might be better to deal with the hundreds (if any first), then run the ones and tens through the same logic. Instead of:

//the case of 10, 11, 12 ,13, .... 19 
if (num < 20) {
    output = ones[num];
    return output;
}

//100 and more
if (numString.length == 3) {
    output = ones[parseInt(numString.charAt(0))] + hundred;
    output += tens[parseInt(numString.charAt(1))];
    output += ones[parseInt(numString.charAt(2))];
    return output;
}

output += tens[parseInt(numString.charAt(0))];
output += ones[parseInt(numString.charAt(1))];

return output;

I would suggest:

// 100 and more
if ( numString.length == 3 ) 
 {
   output  = hundreds[ parseInt( numString.charAt(0) ) ] + hundred ;
   num = num % 100 ;
   numString = num.toString() ;
 }

if ( num < 20 )  
 {
   output += ones[num] ;
 }
else 
 { // 20-99 
   output += tens[ parseInt( numString.charAt(0) ) ] ;
   output += '-' + ones[ parseInt( numString.charAt(1) ) ] ;  
 }

 return output;

It seems to me that the suggested code is both shorter and clearer, but I might be biased ;-)

---

Source: http://javascript.about.com/library/bltoword.htm Smallest script that I found:

  <script type="text/javascript" src="toword.js">
    var words = toWords(12345);
    console.log(words);
  </script>

Enjoy!

---

I tried Muhammad's solution, but had some issues and wanted to use decimals so I made some changes and converted to coffeescript and angular. Please bear in mind that js and coffeescript are not my strong suits, so use with care.

$scope.convert = (number, upper=0) ->
number = +number
# console.log "inside convert and the number is:  " + number

if number < 0
    # console.log 'Number Must be greater than zero = ' + number
    return ''

if number > 100000000000000000000
    # console.log 'Number is out of range = ' + number
    return ''
if isNaN(number)
    console.log("NOT A NUMBER")
    alert("Not a number = ")
    return ''
else
    console.log "at line 88 number is:  " + number
    quintillion = Math.floor(number / 1000000000000000000)
    ### quintillion ###

    number -= quintillion * 1000000000000000000
    quar = Math.floor(number / 1000000000000000)
    # console.log "at line 94 number is:  " + number

    ### quadrillion ###

    number -= quar * 1000000000000000
    trin = Math.floor(number / 1000000000000)
    # console.log "at line 100 number is:  " + number

    ### trillion ###
    number -= trin * 1000000000000
    Gn = Math.floor(number / 1000000000)
    # console.log "at line 105 number is:  " + number

    ### billion ###

    number -= Gn * 1000000000
    million = Math.floor(number / 1000000)
    # console.log "at line 111 number is:  " + number

    ### million ###

    number -= million * 1000000
    Hn = Math.floor(number / 1000)
    # console.log "at line 117 number is:  " + number

    ### thousand ###

    number -= Hn * 1000
    Dn = Math.floor(number / 100)
    # console.log "at line 123 number is:  " + number

    ### Tens (deca) ###

    number = number % 100
    # console.log "at line 128 number is:  " + number

    ### Ones ###
    tn      = Math.floor(number / 10)
    one     = Math.floor(number % 10)
    # tn = Math.floor(number / 1)
    change  = Math.round((number % 1) * 100)
    res     = ''
    # console.log "before ifs"
    if quintillion > 0
        res += $scope.convert(quintillion) + ' Quintillion'
    if quar > 0
        res += $scope.convert(quar) + ' Quadrillion'
    if trin > 0
        res += $scope.convert(trin) + ' Trillion'
    if Gn > 0
        res += $scope.convert(Gn) + ' Billion'
    if million > 0
        res += (if res == '' then '' else ' ') + $scope.convert(million) + ' Million'
    if Hn > 0
        res += (if res == '' then '' else ' ') + $scope.convert(Hn) + ' Thousand'
    if Dn
        res += (if res == '' then '' else ' ') + $scope.convert(Dn) + ' Hundred'
    # console.log "the result is:  " + res
    ones = Array('', 'One', 'Two', 'Three', 'Four', 'Five', 'Six', 'Seven', 'Eight', 'Nine', 'Ten', 'Eleven', 'Twelve', 'Thirteen', 'Fourteen', 'Fifteen', 'Sixteen', 'Seventeen', 'Eightteen', 'Nineteen')
    tens = Array('', '', 'Twenty', 'Thirty', 'Fourty', 'Fifty', 'Sixty', 'Seventy', 'Eigthy', 'Ninety')
    # console.log "the result at 161 is:  " + res
    if tn > 0 or one > 0
        if !(res == '')
            # res += ' and '
            res += ' '
            # console.log "the result at 164 is:  " + res
        if tn < 2
            res += ones[tn * 10 + one]
            # console.log "the result at 168is:  " + res
        else
            res += tens[tn]
            if one > 0
                res += '-' + ones[one]
            # console.log "the result at 173 is:  " + res
    if change > 0
        if res == ''
            res =  change + "/100"
        else
            res += ' and ' + change + "/100"

    if res == ''
        console.log 'Empty = ' + number
        res = ''
    if +upper == 1
        res = res.toUpperCase()
    $scope.newCheck.amountInWords = res
    return res

$scope.is_numeric = (mixed_var) -> # console.log "mixed var is: " + mixed_var (typeof mixed_var == 'number' or typeof mixed_var == 'string') and mixed_var != '' and !isNaN(mixed_var)

---

Here is another version from me with some unit tests.

Don't use it with numbers larger than Number.MAX_SAFE_INTEGER.

describe("English Numerals Converter", function () {
  assertNumeral(0, "zero");
  assertNumeral(1, "one");
  assertNumeral(2, "two");
  assertNumeral(3, "three");
  assertNumeral(4, "four");
  assertNumeral(5, "five");
  assertNumeral(6, "six");
  assertNumeral(7, "seven");
  assertNumeral(8, "eight");
  assertNumeral(9, "nine");
  assertNumeral(10, "ten");
  assertNumeral(11, "eleven");
  assertNumeral(12, "twelve");
  assertNumeral(13, "thirteen");
  assertNumeral(14, "fourteen");
  assertNumeral(15, "fifteen");
  assertNumeral(16, "sixteen");
  assertNumeral(17, "seventeen");
  assertNumeral(18, "eighteen");
  assertNumeral(19, "nineteen");
  assertNumeral(20, "twenty");
  assertNumeral(21, "twenty-one");
  assertNumeral(22, "twenty-two");
  assertNumeral(23, "twenty-three");
  assertNumeral(30, "thirty");
  assertNumeral(37, "thirty-seven");
  assertNumeral(40, "forty");
  assertNumeral(50, "fifty");
  assertNumeral(60, "sixty");
  assertNumeral(70, "seventy");
  assertNumeral(80, "eighty");
  assertNumeral(90, "ninety");
  assertNumeral(99, "ninety-nine");
  assertNumeral(100, "one hundred");
  assertNumeral(101, "one hundred and one");
  assertNumeral(102, "one hundred and two");
  assertNumeral(110, "one hundred and ten");
  assertNumeral(120, "one hundred and twenty");
  assertNumeral(121, "one hundred and twenty-one");
  assertNumeral(199, "one hundred and ninety-nine");
  assertNumeral(200, "two hundred");
  assertNumeral(999, "nine hundred and ninety-nine");
  assertNumeral(1000, "one thousand");
  assertNumeral(1001, "one thousand and one");
  assertNumeral(1011, "one thousand and eleven");
  assertNumeral(1111, "one thousand and one hundred and eleven");
  assertNumeral(9999, "nine thousand and nine hundred and ninety-nine");
  assertNumeral(10000, "ten thousand");
  assertNumeral(20000, "twenty thousand");
  assertNumeral(21000, "twenty-one thousand");
  assertNumeral(90000, "ninety thousand");
  assertNumeral(90001, "ninety thousand and one");
  assertNumeral(90100, "ninety thousand and one hundred");
  assertNumeral(90901, "ninety thousand and nine hundred and one");
  assertNumeral(90991, "ninety thousand and nine hundred and ninety-one");
  assertNumeral(90999, "ninety thousand and nine hundred and ninety-nine");
  assertNumeral(91000, "ninety-one thousand");
  assertNumeral(99999, "ninety-nine thousand and nine hundred and ninety-nine");
  assertNumeral(100000, "one hundred thousand");
  assertNumeral(999000, "nine hundred and ninety-nine thousand");
  assertNumeral(1000000, "one million");
  assertNumeral(10000000, "ten million");
  assertNumeral(100000000, "one hundred million");
  assertNumeral(1000000000, "one billion");
  assertNumeral(1000000000000, "one trillion");
  assertNumeral(1000000000000000, "one quadrillion");
  assertNumeral(1000000000000000000, "one quintillion");
  assertNumeral(1000000000000000000000, "one sextillion");

  assertNumeral(-1, "minus one");
  assertNumeral(-999, "minus nine hundred and ninety-nine");

  function assertNumeral(number, numeral) {
    it(number + " is " + numeral, function () {
      expect(convert(number)).toBe(numeral);
    });
  }
});


function convert(n) {
  let NUMERALS = [
    {value: 1000000000000000000000, str: "sextillion"},
    {value: 1000000000000000000, str: "quintillion"},
    {value: 1000000000000000, str: "quadrillion"},
    {value: 1000000000000, str: "trillion"},
    {value: 1000000000, str: "billion"},
    {value: 1000000, str: "million"},
    {value: 1000, str: "thousand"},
    {value: 100, str: "hundred"},
    {value: 90, str: "ninety"},
    {value: 80, str: "eighty"},
    {value: 70, str: "seventy"},
    {value: 60, str: "sixty"},
    {value: 50, str: "fifty"},
    {value: 40, str: "forty"},
    {value: 30, str: "thirty"},
    {value: 20, str: "twenty"},
    {value: 19, str: "nineteen"},
    {value: 18, str: "eighteen"},
    {value: 17, str: "seventeen"},
    {value: 16, str: "sixteen"},
    {value: 15, str: "fifteen"},
    {value: 14, str: "fourteen"},
    {value: 13, str: "thirteen"},
    {value: 12, str: "twelve"},
    {value: 11, str: "eleven"},
    {value: 10, str: "ten"},
    {value: 9, str: "nine"},
    {value: 8, str: "eight"},
    {value: 7, str: "seven"},
    {value: 6, str: "six"},
    {value: 5, str: "five"},
    {value: 4, str: "four"},
    {value: 3, str: "three"},
    {value: 2, str: "two"},
    {value: 1, str: "one"}
  ];

  if (n < 0) {
    return "minus " + convert(-n);
  } else if (n === 0) {
    return "zero";
  } else {
    let result = "";
    for (let numeral of NUMERALS) {
      if (n >= numeral.value) {
        if (n < 100) {
          result += numeral.str;
          n -= numeral.value;
          if (n > 0) result += "-";
        } else {
          let times = Math.floor(n / numeral.value);
          result += convert(times) + " " + numeral.str;
          n -= numeral.value * times;
          if (n > 0) result += " and ";
        }
      }
    }
    return result;
  }
}

---

<script src="http://www.ittutorials.in/js/demo/numtoword.js" type="text/javascript"></script>
    HTML - Convert numbers to words using JavaScript</h1>
<input id="Text1" type="text" onkeypress="return onlyNumbers(this.value);" onkeyup="NumToWord(this.value,'divDisplayWords');"
    maxlength="9" style="background-color: #efefef; border: 2px solid #CCCCC; font-size: large" />
<br />
<br />
<div id="divDisplayWords" style="font-size: 13; color: Teal; font-family: Arial;">
</div>

---

I think, I have solution that's simpler and easier to understand; it goes by slicing the number, it works up to 99 lakhs crore.

function convert_to_word(num, ignore_ten_plus_check) {

var ones = [];
var tens = [];
var ten_plus = [];
ones["1"] = "one";
ones["2"] = "two";
ones["3"] = "three";
ones["4"] = "four";
ones["5"] = "five";
ones["6"] = "six";
ones["7"] = "seven";
ones["8"] = "eight";
ones["9"] = "nine";

ten_plus["10"] = "ten";
ten_plus["11"] = "eleven";
ten_plus["12"] = "twelve";
ten_plus["13"] = "thirteen";
ten_plus["14"] = "fourteen";
ten_plus["15"] = "fifteen";
ten_plus["16"] = "sixteen";
ten_plus["17"] = "seventeen";
ten_plus["18"] = "eighteen";
ten_plus["19"] = "nineteen";

tens["1"] = "ten";
tens["2"] = "twenty";
tens["3"] = "thirty";
tens["4"] = "fourty";
tens["5"] = "fifty";
tens["6"] = "sixty";
tens["7"] = "seventy";
tens["8"] = "eighty";
tens["9"] = "ninety";   

    var len = num.length;

    if(ignore_ten_plus_check != true && len >= 2) {
        var ten_pos = num.slice(len - 2, len - 1);
        if(ten_pos == "1") {
            return ten_plus[num.slice(len - 2, len)];
        } else if(ten_pos != 0) {
            return tens[num.slice(len - 2, len - 1)] + " " + ones[num.slice(len - 1, len)];
        }
    }

    return ones[num.slice(len - 1, len)];

}

function get_rupees_in_words(str, recursive_call_count) {
  if(recursive_call_count > 1) {
        return "conversion is not feasible";
    }
    var len = str.length;
    var words = convert_to_word(str, false);
    if(len == 2 || len == 1) {
    if(recursive_call_count == 0) {
        words = words +" rupees";
    }
        return words;
    }
    if(recursive_call_count == 0) {
        words = " and " + words +" rupees";
    }



var hundred = convert_to_word(str.slice(0, len-2), true);
  words = hundred != undefined ? hundred + " hundred " + words : words;
    if(len == 3) {
        return words;
    }

var thousand = convert_to_word(str.slice(0, len-3), false);
words = thousand != undefined ? thousand  + " thousand " + words : words;
if(len <= 5) {
    return words;
}

var lakh = convert_to_word(str.slice(0, len-5), false);
words =  lakh != undefined ? lakh + " lakh " + words : words;
if(len <= 7) {
    return words;
}

recursive_call_count = recursive_call_count + 1;
return get_rupees_in_words(str.slice(0, len-7), recursive_call_count) + " crore " + words;
}

Please check out my code pen

---

If anybody ever wants to do this but in Spanish (en español), here's my code based on Hardik's

function num2str(num, moneda) {
    moneda = moneda || (num !== 1 ? "pesos" : "peso");
    var fraction = Math.round(__cf_frac(num) * 100);
    var f_text = " (" + pad(fraction, 2) + "/100 M.N.)";


    return __cf_convert_number(num) + " " + moneda + f_text;
}

function __cf_frac(f) {
    return f % 1;
}

function __cf_convert_number(number) {
    if ((number < 0) || (number > 999999999)) {
        throw Error("N\u00famero fuera de rango");
    }
    var millon = Math.floor(number / 1000000);
    number -= millon * 1000000;
    var cientosDeMiles = Math.floor(number / 100000);
    number -= cientosDeMiles * 100000;
    var miles = Math.floor(number / 1000);
    number -= miles * 1000;
    var centenas = Math.floor(number / 100);
    number = number % 100;
    var tn = Math.floor(number / 10);
    var one = Math.floor(number % 10);
    var res = "";

    var cientos = Array("", "cien", "doscientos", "trescientos", "cuatrocientos", "quinientos", "seiscientos", "setecientos", "ochocientos", "novecientos");
    if (millon > 0) {
        res += (__cf_convert_number(millon) + (millon === 1 ? " mill\u00f3n" : " millones"));
    }
    if (cientosDeMiles > 0) {
        res += (((res == "") ? "" : " ") +
            cientos[cientosDeMiles] + (miles > 0 || centenas > 0 || tn > 0 || one < 0 ? (cientosDeMiles == 1 ? "to " : " ") : ""));
    }
    if (miles > 0) {
        res += (((res == "") ? "" : " ") +
            __cf_convert_number(miles) + " mil");
    }
    if (centenas) {
        res += (((res == "") ? "" : " ") +
            cientos[centenas] + (tn > 0 || one > 0 ? (centenas > 1 ? " " : "to ") : ""));
    }


    var ones = Array("", "un", "dos", "tres", "cuatro", "cinco", "seis", "siete", "ocho", "nueve", "diez", "once", "doce", "trece", "catorce", "quince", "dieciseis", "diecisiete", "dieciocho", "diecinueve");
    var tens = Array("", "", "veinte", "treinta", "cuarenta", "cincuenta", "sesenta", "setenta", "ochenta", "noventa");

    if (tn > 0 || one > 0) {
        if (tn < 2) {
            res += ones[tn * 10 + one];
        }
        else {
            if (tn === 2 && one > 0)
                res += "veinti" + ones[one];
            else {
                res += tens[tn];
                if (one > 0) {
                    res += (" y " + ones[one]);
                }
            }
        }
    }

    if (res == "") {
        res = "cero";
    }
    return res.replace("  ", " ");
}

function pad(num, largo, char) {
    char = char || '0';
    num = num + '';
    return num.length >= largo ? num : new Array(largo - num.length + 1).join(char) + num;
}

Result:

num2str(123456789)
"ciento veintitres millones cuatrocientos cincuenta y seis mil setecientos ochenta y nueve pesos (00/100 M.N.)"

---

I am providing here my solution for converting numbers to the equivalent English words using the Single Loop String Triplets (SLST) Method which I have published and explained in detail here at Code Review with illustration graphics.

Simple Number to Words using a Single Loop String Triplets in JavaScript

The concept is simple and easily coded and is also very efficient and fast. The code is very short compared with other alternative methods described in this article.

The concept also permits the conversion of very vary large numbers as it does not rely on using the numeric/math function of the language and therefore avoids any limitations.

The Scale Array may be increased by adding more scale names if required after "Decillion".

A sample test function is provided below to generate numbers from 1 to 1099 as an example.

A full fancy version is available that caters for adding the word "and" and commas between the scales and numbers to align with the UK and US ways of spelling the numbers.

Hope this is useful.

/************************************************************/
function NumToWordsInt(NumIn) {
/************************************************************
* Convert Integer Numbers to English Words
* Using the Single Loop String Triplets Method
* @Param : {Number}  The number to be converted
*                    For large numbers use a string
* @Return: {String}  Wordified Number (Number in English Words)
* @Author: Mohsen Alyafei 10 July 2019
* @Notes : Call separately for whole and for fractional parts.
*          Scale Array may be increased by adding more scale
*          names if required after Decillion.
/************************************************************/
  
 if (NumIn==0) return "Zero";
 var  Ones  = ["", "One", "Two", "Three", "Four", "Five", "Six", "Seven", "Eight", "Nine", "Ten", "Eleven", "Twelve", "Thirteen", "Fourteen", "Fifteen", "Sixteen", "Seventeen", "Eighteen", "Nineteen"],
      Tens  = ["", "", "Twenty", "Thirty", "Forty", "Fifty", "Sixty", "Seventy", "Eighty", "Ninety"],
      Scale = ["", "Thousand", "Million", "Billion", "Trillion", "Quadrillion", "Quintillion", "Sextillion", "Septillion", "Octillion", "Nonillion", "Decillion"],
      N1, N2, Sep, j, i, h, Trplt, tns="", NumAll = "";
 NumIn += "";                                            // Make NumIn a String
//----------------- code starts -------------------
 NumIn = "0".repeat(NumIn.length * 2 % 3) + NumIn;       //Create shortest string triplets 0 padded
 j = 0;                                                  //Start with the highest triplet from LH
    for (i = NumIn.length / 3 - 1; i >= 0; i--) {        //Loop thru number of triplets from LH most
      Trplt = NumIn.substring(j, j + 3);                 //Get a triplet number starting from LH
      if (Trplt !="000") {                               //Skip empty trplets
        Sep = Trplt[2] !="0" ? "-":" ";                  //Dash only for 21 to 99
        N1 = Number(Trplt[0]);                           //Get Hundreds digit
        N2 = Number(Trplt.substr(1));                    //Get 2 lowest digits (00 to 99) 
        tns = N2 > 19 ? Tens[Number(Trplt[1])] + Sep + Ones[Number(Trplt[2])] : Ones[N2];
        NumAll += ((h = N1>0 ? Ones[N1] + " Hundred": "") + " " + tns).trim() + " " + Scale[i]+ " "; 
      }
      j += 3;                                            //Next lower triplets (move to RH)
    }
//----------------- code Ends --------------------
 return NumAll.trim();                                   //Return trimming excess spaces if any
}



// ----------------- test sample -----------------
console.log(NumToWordsInt(67123))
console.log(NumToWordsInt(120003123))
console.log(NumToWordsInt(123999))
console.log(NumToWordsInt(789123))
console.log(NumToWordsInt(100178912))
console.log(NumToWordsInt(777))
console.log(NumToWordsInt(999999999))
console.log(NumToWordsInt(45))

---

I know this has been answered but I had been working on this before seeing the question. Doesn't have some small errors found in other answers. Supports up to vigintillion.

const num_text = num => {
    const ones = {1: "one", 2: "two", 3: "three", 4: "four", 5: "five", 6: "six", 7: "seven", 8: "eight", 9: "nine"}, _tens = ["ten", "eleven", "twelve", "thirteen", "fourteen", "fifteen", "sixteen", "seventeen", "eighteen", "nineteen"], tens = {2: "twenty", 3: "thirty", 4: "forty", 5: "fifty", 6: "sixty", 7: "seventy", 8: "eighty", 9: "ninety"}, above_tens = ["thousand", "million", "billion", "trillion", "quadrillion", "quintillion", "sextillion", "septillion", "octillion", "nonillion", "decillion", "undecillion", "duodecillion", "tredecillion", "quattuordecillion", "quindecillion", "sexdecillion", "septendecillion", "octodecillion", "novemdecillion", "vigintillion"]; 

    var result = []; 

    if (/^0+$/g.test(num)) return "zero"; 

    num = num.replace(/^0+/g, "").split(/(?=(?:...)*$)/); 
    
    for (var count = 0; count < num.length; count++){
        var _result = "", _num = num[count]; 
        
        _num = _num.replace(/^0+/g, ""); 
        if (_num.length == 3){
            _result += ones[_num[0]] + " hundred"; 
            _num = _num.substring(1, 3).replace(/^0+/g, ""); 
            if (_num.length > 0) _result += " and "; 
        }
        if (_num.length == 1){
            _result += ones[_num]; 
        }else if (_num.length == 2){
            if (_num[0] == "1"){
                _result += _tens[_num[1]]; 
            }else if (/.0/g.test(_num)){
                _result += tens[_num[0]]; 
            }else{
                _result += tens[_num[0]] + " " + ones[_num[1]]; 
            }
        }
        
        if (_result != ""){
            if (num.length - count - 2 >= 0) _result += " " + above_tens[num.length - count - 2]; 
            result.push(_result); 
        }
    }

    if (result[result.length - 1].includes("and") || result.length == 1) return result.join(", "); 
    return result.slice(0, result.length - 1).join(", ") + " and " + result[result.length - 1]; 
}

<input id="input">
<button onclick="document.getElementById('result').innerHTML = num_text(document.getElementById('input').value)">Convert</button>
<div id="result"></div>

---

https://stackoverflow.com/a/69243038/8784402

TypeScript Version Based on ES2022 + Fastest

Test on Typescript Playground

Hindi Version

class N2WHindi {
  // "शून्य"
  private static readonly zeroTo99: string[] =
    '|एक|दो|तीन|चार|पाँच|छः|सात|आठ|नौ|दश|ग्यारह|बारह|तेरह|चौदह|पन्द्रह|सोलह|सत्रह|अठारह|उन्नीस|बीस|इक्कीस|बाईस|तेईस|चौबीस|पच्चीस|छब्बीस|सत्ताईस|अट्ठाईस|उनतीस|तीस|इकतीस|बत्तीस|तैंतीस|चौंतीस|पैंतीस|छत्तीस|सैंतीस|अड़तीस|उनतालीस|चालीस|इकतालीस|बयालीस|तैंतालीस|चौवालीस|पैंतालीस|छियालीस|सैंतालीस|अड़तालीस|उनचास|पचास|इक्यावन|बावन|तिरपन|चौवन|पचपन|छप्पन|सत्तावन|अट्ठावन|उनसठ|साठ|इकसठ|बासठ|तिरसठ|चौंसठ|पैंसठ|छियासठ|सड़सठ|अड़सठ|उनहत्तर|सत्तर|इकहत्तर|बहत्तर|तिहत्तर|चौहत्तर|पचहत्तर|छिहत्तर|सतहत्तर|अठहत्तर|उन्यासी|अस्सी|इक्यासी|बयासी|तिरासी|चौरासी|पचासी|छियासी|सत्तासी|अट्ठासी|नवासी|नब्बे|इक्यानबे|बानबे|तिरानबे|चौरानबे|पंचानबे|छियानबे|सत्तानबे|अट्ठानबे|निन्यान्बे'.split(
      '|'
    );

  private static readonly place: string[] = 'हज़ार|लाख|करोड़|अरब|खरब|नील'.split('|');

  public static convert(x: string): string {
    let n: number = x.length;
    x = n == 0 ? '00' : n == 1 || n % 2 == 0 ? '0' + x : x;
    n = x.length;
    let r: string = N2WHindi.zeroTo99[x.charCodeAt((n -= 2)) * 10 + x.charCodeAt(n + 1) - 528];
    if (n > 0) {
      const v: string = N2WHindi.zeroTo99[x.charCodeAt((n -= 1)) - 48];
      if (v) r = v + ' सौ ' + r;
    }
    for (let i = 0; n > 0; i++) {
      const v: string = N2WHindi.zeroTo99[x.charCodeAt((n -= 2)) * 10 + x.charCodeAt(n + 1) - 528];
      if (v) r = v + ' ' + N2WHindi.place[i] + (r ? ' ' + r : '');
    }
    return r;
  }
}

Indian English Version

class N2WIndian {
  private static readonly zeroTo99: string[] = [];
  private static readonly place: string[] = 'Thousand|Lakh|Crore|Arab|Kharab|Nil'.split('|');

  static {
    const ones: string[] =
      '|One|Two|Three|Four|Five|Six|Seven|Eight|Nine|Ten|Eleven|Twelve|Thirteen|Fourteen|Fifteen|Sixteen|Seventeen|Eighteen|Nineteen'.split(
        '|'
      );

    const tens: string[] = '||Twenty|Thirty|Forty|Fifty|Sixty|Seventy|Eighty|Ninety'.split('|');

    for (let i = 0; i < 100; i++) {
      const t: number = Math.floor(i / 10);
      const o: number = i % 10;
      N2WIndian.zeroTo99.push(t < 2 ? ones[i] : tens[t] + (o ? ' ' + ones[o] : ''));
    }
  }

  public static convert(x: string): string {
    let n: number = x.length;
    x = n == 0 ? '00' : n == 1 || n % 2 == 0 ? '0' + x : x;
    n = x.length;
    let r = N2WIndian.zeroTo99[x.charCodeAt((n -= 2)) * 10 + x.charCodeAt(n + 1) - 528];
    if (n >= 1) {
      const v: string = N2WIndian.zeroTo99[x.charCodeAt((n -= 1)) - 48];
      if (v) r = v + ' Hundred ' + r;
    }
    for (let i = 0; n > 0; i++) {
      const v: string = N2WIndian.zeroTo99[x.charCodeAt((n -= 2)) * 10 + x.charCodeAt(n + 1) - 528];
      if (v) r = v + ' ' + N2WIndian.place[i] + (r ? ' ' + r : '');
    }
    return r;
  }
}

International Version

class N2WIntl {
  private static readonly zeroTo999: string[] = [];

  private static readonly place =
    '|Thousand|Million|Billion|Trillion|Quadrillion|Quintillion|Sextillion|Septillion|Octillion|Nonillion|Decillion|Undecillion|Duodecillion|Tredecillion|Quattuordecillion|Quindecillion|Sedecillion|Septendecillion|Octodecillion|Novendecillion|Vigintillion|Unvigintillion|Duovigintillion|Tresvigintillion|Quattuorvigintillion|Quinvigintillion|Sesvigintillion|Septemvigintillion|Octovigintillion|Novemvigintillion|Trigintillion|Untrigintillion|Duotrigintillion|Trestrigintillion|Quattuortrigintillion|Quintrigintillion|Sestrigintillion|Septentrigintillion|Octotrigintillion|Noventrigintillion|Quadragintillion'.split(
      '|'
    );

  static {
    const ones =
      '|One|Two|Three|Four|Five|Six|Seven|Eight|Nine|Ten|Eleven|Twelve|Thirteen|Fourteen|Fifteen|Sixteen|Seventeen|Eighteen|Nineteen'.split(
        '|'
      );
    const tens = '||Twenty|Thirty|Forty|Fifty|Sixty|Seventy|Eighty|Ninety'.split('|');
    for (let i = 0; i < 100; i++) {
      const t = Math.floor(i / 10);
      const o = i % 10;
      N2WIntl.zeroTo999[i] = t < 2 ? ones[i] : tens[t] + (o == 0 ? '' : ' ' + ones[o]);
    }
    for (let i = 100; i < 1000; i++) {
      const h = Math.floor(i / 100);
      const t = Math.floor(i / 10) % 10;
      const o = i % 10;
      const r = N2WIntl.zeroTo999[h] + ' Hundred';
      N2WIntl.zeroTo999[i] = t == 0 && o == 0 ? r : r + ' ' + N2WIntl.zeroTo999[t * 10 + o];
    }
  }

  public static convert(x: string): string {
    let n = x.length;
    x = n == 0 ? '000' : ((n % 3 === 1) ? '00' : (n % 3 === 2) ? '0' : '') + x;
    n = x.length;
    let r: string = '';
    for (let i = 0; n > 0; i++) {
      const v: string =
        N2WIntl.zeroTo999[x.charCodeAt((n -= 3)) * 100 + x.charCodeAt(n + 1) * 10 + x.charCodeAt(n + 2) - 5328];
      if (v) r = v + (i ? ' ' + N2WIntl.place[i] : '') + (r ? ' ' + r : '');

    }
    return r;
  }
}

const test = () => {
  {
    let n = 5000000;
    const test: string = '1234567890';
    const t0 = performance.now();
    while (n-- > 0) {
      N2WHindi.convert(test);
    }
    const t1 = performance.now();
    console.log('1234567890 to 5 Million times: ' + (t1 - t0) + 'ms');
    console.log('10^15 -1 :\n' + '9'.repeat(15) + '\n' + N2WHindi.convert('9'.repeat(15)));
  }

  {
    let n = 5000000;
    const test: string = '1234567890';
    const t0 = performance.now();
    while (n-- > 0) {
      N2WIndian.convert(test);
    }
    const t1 = performance.now();
    console.log('1234567890 to 5 Million times: ' + (t1 - t0) + 'ms');
    console.log('10^15 -1 :\n' + '9'.repeat(15) + '\n' + N2WIndian.convert('9'.repeat(15)));
  }

  {
    let n = 5000000;
    const test: string = '1234567890';
    const t0 = performance.now();
    while (n-- > 0) {
      N2WIntl.convert(test);
    }
    const t1 = performance.now();
    console.log('1234567890 to 5 Million times: ' + (t1 - t0) + 'ms');
    console.log('10^126 -1 :\n' + '9'.repeat(126) + '\n' + N2WIntl.convert('9'.repeat(126)));
  }
};

test();

Example to convert currency

const [r, p] = "23.54".split('.');
console.log(`${N2WHindi.convert(r)} रुपया और ${N2WHindi.convert(p)} पैसा`)
console.log(`${N2WIndian.convert(r)} Rupees and ${N2WIndian.convert(p)} Paisa`)
console.log(`${N2WIntl.convert(r)} Dollars and ${N2WIntl.convert(p)} Cents`)

---

I think this will help you

    aTens = [ "Twenty", "Thirty", "Forty", "Fifty", "Sixty", "Seventy","Eighty", "Ninety"];

    aOnes = [ "Zero", "One", "Two", "Three", "Four", "Five", "Six", "Seven", "Eight", "Nine", "Ten", "Eleven", "Twelve", "Thirteen", "Fourteen", "Fifteen", "Sixteen", "Seventeen", "Eighteen", "Nineteen" ];
    var aUnits = "Thousand";
    function convertnumbertostring(){
       var num=prompt('','enter the number');
       var j=6;
       if(num.length<j){
       var y = ConvertToWords(num);
       alert(y);
       }else{
          alert('Enter the number of 5 letters')
       }
    };
    function ConvertToHundreds(num)
    {
       var cNum, nNum;
       var cWords = "";
       if (num > 99) {
          /* Hundreds. */
          cNum = String(num);
          nNum = Number(cNum.charAt(0));
          cWords += aOnes[nNum] + " Hundred";
          num %= 100;
          if (num > 0){
             cWords += " and "
          }
       }

       if (num > 19) {
          /* Tens. */
          cNum = String(num);
          nNum = Number(cNum.charAt(0));
          cWords += aTens[nNum - 2];
          num %= 10;
          if (num > 0){
             cWords += "-";
          }
       }
       if (num > 0) {
          /* Ones and teens. */
          nNum = Math.floor(num);
          cWords += aOnes[nNum];
       }
       return(cWords);

    }
    function ConvertToWords(num)
    {
       var cWords;
       for (var i = 0; num > 0; i++) { 
           if (num % 1000 > 0) {
              if (i != 0){
                 cWords = ConvertToHundreds(num) + " " + aUnits + " " + cWords;
              }else{
                 cWords = ConvertToHundreds(num) + " ";
              }        
           }
           num = (num / 1000);
       }
         return(cWords);
    }