https://www.jianshu.com/p/837b584e1bdd
https://blog.fundebug.com/2019/01/15/diffrences-of-browser-and-node-in-event-loop/
浏览器： https://image.fundebug.com/2019-01-14-007.gif
node: https://image.fundebug.com/2019-01-14-008.gif