//num 是傳過來的值，del是要保留幾位

function valueFmt(num, del) {
    if (num != '') {
        if (del != 0) {
            num = parseFloat(num).toFixed(del);
        }
        var source = String(num).split(".");
        source[0] = source[0].replace(new RegExp('(\\d)(?=(\\d{3})+$)', 'ig'), "$1,");
        return source.join(".") == "NaN" ? "0.00" : source.join(".");
    }
};

var num = 2.00;

var result=valueFmt(num,2);

console.log(result);//結果是：2.00