YUI number format supporting negativeFormat

/**
 * Takes a native JavaScript Number and formats to string for display to user.
 *
 * @method format
 * @param nData {Number} Number.
 * @param oConfig {Object} (Optional) Optional configuration values:
 *  <dl>
 *   <dt>prefix {String}</dd>
 *   <dd>String prepended before each number, like a currency designator "$"</dd>
 *   <dt>decimalPlaces {Number}</dd>
 *   <dd>Number of decimal places to round.</dd>
 *   <dt>decimalSeparator {String}</dd>
 *   <dd>Decimal separator</dd>
 *   <dt>thousandsSeparator {String}</dd>
 *   <dd>Thousands separator</dd>
 *   <dt>suffix {String}</dd>
 *   <dd>String appended after each number, like " items" (note the space)</dd>
 *   <dt>negativeFormat</dt>
 *   <dd>String used as a guide for how to indicate negative numbers.  The first '#' character in the string will be replaced by the number.  Default '-#'.</dd>
 *  </dl>
 * @return {String} Formatted number for display. Note, the following values
 * return as "": null, undefined, NaN, "".     
 */
YAHOO.util.Number.format = function (n,cfg) {
    if (!isFinite(+n)) {
        return '';
    }

    n   = !isFinite(+n) ? 0 : +n;
    cfg = YAHOO.lang.merge(YAHOO.util.Number.format.defaults, (cfg || {}));

    var neg    = n < 0,        absN   = Math.abs(n),
        places = cfg.decimalPlaces,
        sep    = cfg.thousandsSeparator,
        s, bits, i;

    if (places < 0) {
        // Get rid of the decimal info
        s = absN - (absN % 1) + '';
        i = s.length + places;

        // avoid 123 vs decimalPlaces -4 (should return "0")
        if (i > 0) {
                // leverage toFixed by making 123 => 0.123 for the rounding
                // operation, then add the appropriate number of zeros back on
            s = Number('.' + s).toFixed(i).slice(2) +
                new Array(s.length - i + 1).join('0');
        } else {
            s = "0";
        }
    } else {        // There is a bug in IE's toFixed implementation:
        // for n in {(-0.94, -0.5], [0.5, 0.94)} n.toFixed() returns 0
        // instead of -1 and 1. Manually handle that case.
        s = absN < 1 && absN >= 0.5 && !places ? '1' : absN.toFixed(places);
    }

    if (absN > 1000) {
        bits  = s.split(/\D/);
        i  = bits[0].length % 3 || 3;

        bits[0] = bits[0].slice(0,i) +
                  bits[0].slice(i).replace(/(\d{3})/g, sep + '$1');

        s = bits.join(cfg.decimalSeparator);
    }

    s = cfg.prefix + s + cfg.suffix;

    return neg ? cfg.negativeFormat.replace(/#/,s) : s;
};
YAHOO.util.Number.format.defaults = {
    decimalSeparator : '.',
    decimalPlaces    : null,
    thousandsSeparator : ',',
    prefix : '',
    suffix : '',
    negativeFormat : '-#'
};