千分位分隔符，支持自定义位数

thousandsSeparator(num, point) {
    let _point = (point === 0) ? 0 : (point || 2),
      _num = String(num).indexOf('.')>-1 ? num.toFixed(_point) : num,
      str = _num.toString(),
      reg = str.indexOf(".") > -1 ? /(\d)(?=(\d{3})+\.)/g : /(\d)(?=(?:\d{3})+$)/g;
    return str.replace(reg, "$1,");
  }