resource:
official dc: https://html.spec.whatwg.org/multipage/webappapis.html#event-loop-processing-model
UC 国际 https://www.jianshu.com/writer#/notebooks/13486709/notes/22010355
图解

图片发自简书App

图片发自简书App

图片发自简书App

图片发自简书App
SetTimeout:
. problem:
- There is 4ms gap when a next cb is executed

- this can be bind, can't be