Convert numbers to English words

numbertowords.js

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) {
            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, ' ');
}