_format_number_as_us_currency_javascript

## _format_number_as_us_currency_javascript
Format number as US currency

Format an unsigned integer or float to US currency string, e.g. $1,234,567.89.

1. Convert number to string.

2. If string contains period split at the period.
    1234567.89 => string a) 1234567, string b) 89

3. If string a is 4 character or longer insert ',' every third character.
    1234567 => 1,234,567

4. Concatenate string a and string b.
    1,234,567 + 89 => 1,234,567.89

5. If requested, prepend '$' to number sting.
    1,234,567.89 => $1,234,567.89

## formatCostNumber.js
function formatCostNumber(amount, curSym) {
    var unformattedNumber = amount || null;
    var addSymbol = curSym || false;
    var formattedNumber = "0";

    var formatNumber = function(toFormat) {
            if (toFormat.length >= 4) {

                // Pars string in revers, track number of tiems looped
                for (var i = toFormat.length, hops = 0, turns = 0; i >= 1; i--, turns++) {

                    // If moved 3 characters, insert comma
                    if (hops === 3 && toFormat.charAt(i) !== ',') {
                        toFormat = toFormat.substr(0, i) + ',' + toFormat.substr(i);

                        // Reset count since last ',' insertion, update string lenght
                        hops = 0;
                        i = toFormat.length - turns;
                    } else {
                        hops++;
                    }
                }
            }

            return toFormat;
        };

    if (unformattedNumber !== null && typeof +unformattedNumber === 'number') {
        // Convert number to string.
        var numberString = unformattedNumber.toString();

        // If string has a number split at '.' and format string before period
        if (numberString.indexOf('.') !== -1) {
            numberString = numberString.split('.');
            formattedNumber = formatNumber(numberString[0]);
            formattedNumber = formattedNumber + '.' + numberString[1];
        } else {
            formattedNumber = formatNumber(numberString);
        }
    }

    // Add a currency symbol
    return (addSymbol) ? '$' + formattedNumber : formattedNumber;
}