JavaScript金額的格式化函數

function formatNumber(num, pattern) {
            var strarr = num ? num.toString().split('.') : ['0'];
            var fmtarr = pattern ? pattern.split('.') : [''];
            var retstr = '';

            // 整數部分  
            var str = strarr[0];
            var fmt = fmtarr[0];
            var i = str.length - 1;
            var comma = false;
            for (var f = fmt.length - 1; f >= 0; f--) {
                switch (fmt.substr(f, 1)) {
                    case '#':
                        if (i >= 0) retstr = str.substr(i--, 1) + retstr;
                        break;
                    case '0':
                        if (i >= 0) retstr = str.substr(i--, 1) + retstr;
                        else retstr = '0' + retstr;
                        break;
                    case ',':
                        comma = true;
                        retstr = ',' + retstr;
                        break;
                }
            }
            if (i >= 0) {
                if (comma) {
                    var l = str.length;
                    for (; i >= 0; i--) {
                        retstr = str.substr(i, 1) + retstr;
                        if (i > 0 && ((l - i) % 3) == 0) retstr = ',' + retstr;
                    }
                }
                else retstr = str.substr(0, i + 1) + retstr;
            }

            retstr = retstr + '.';
            // 處理小數部分  
            str = strarr.length > 1 ? strarr[1] : '';
            fmt = fmtarr.length > 1 ? fmtarr[1] : '';
            i = 0;
            for (var f = 0; f < fmt.length; f++) {
                switch (fmt.substr(f, 1)) {
                    case '#':
                        if (i < str.length) retstr += str.substr(i++, 1);
                        break;
                    case '0':
                        if (i < str.length) retstr += str.substr(i++, 1);
                        else retstr += '0';
                        break;
                }
            }
            return retstr.replace(/^,+/, '').replace(//.$/, '');
        }