A JavaScript function for converting numbers (21) to words (twenty-one). It works for numbers up to 999, but it can be transformed to support numbers in the thousands too.

1.<script type="text/javascript">
2.var SingleDigits = new Array("Zero", "One", "Two", "Three", "Four", "Five", "Six", "Seven", "Eight", "Nine", "Ten", "Eleven", "Twelve", "Thirteen", "Fourteen", "Fifteen", "Sixteen", "Seventeen", "Eighteen", "Nineteen");
3.var DoubleDigits = new Array("Twenty", "Thirty", "Forty", "Fifty", "Sixty", "Seventy", "Eighty", "Ninety");
4. 
5.function DigitsToWords(Digits)
6.{
7.        var Words = "";
8.        var St;
9.        if (Digits > 999)
10.        {
11.                return "The number exceeds 999.";
12.        }
13.        if (Digits == 0)
14.        {
15.                return SingleDigits[0];
16.        }
17.        for (var i = 9; i >= 1; i--)
18.        {
19.                if (Digits >= i * 100)
20.                {
21.                        Words += SingleDigits[i];
22.                        St = 1;
23.                        Words += " hundred";
24.                        if (Digits != i * 100) Words += " and ";
25.                        {
26.                                Digits -= i*100;
27.                        }
28.                        i=0;
29.                }
30.        }
31.       
32.        for (var i = 9; i >= 2; i--)
33.        {
34.                if (Digits >= i * 10)
35.                {
36.                    Words += (St?DoubleDigits[i-2].toLowerCase():DoubleDigits[i-2]);
37.                        St = 1;
38.                        if (Digits != i * 10) Words += "-";
39.                        {
40.                                Digits -= i*10;
41.                        }
42.                        i=0;
43.                }
44.        }
45.      
46.        for (var i = 1; i < 20; i++)
47.        {
48.                if (Digits == i)
49.                {
50.                    Words += (St?SingleDigits[i].toLowerCase():SingleDigits[i]);
51.                }
52.        }
53.        return Words;
54.}
55.
56.alert("Are you over " + DigitsToWords(21) + "?");
57.</script>