JavaScript 使小數點後面不足2位數補0

function formatnumber(value, num){
  let _value = value.toString();
  let _dot = _value.indexOf(".");
  let _valueLen  = _value.length;
  if (num == 0) {
      if (_dot != -1) {
          _value = _value.substring(0, _dot);
      }
  } else {//若是沒有小數點
      if (_dot == -1) {
          _value = _value + ".";
          for (let i = 1; i <= num; i++) {
              _value = _value + "0";
          }
      } else {//有小數點，超出位數自動截取，不然補0
          _value = _value.substring(0, _dot + num + 1);
          for (let i = _valueLen; i <= _dot + num; i++) {
              _value = _value + "0";
          }
      }
  }
  return _value;
}

formatnumber(3.1,2)複製代碼