https://single9.net/2015/12/nodejs-%e7%82%ba-console-log-%e5%8a%a0%e4%b8%8a%e6%99%82%e9%96%93%e8%88%87%e6%aa%94%e6%a1%88%e7%b4%80%e9%8c%84%e3%80%82/