异步与同步
https://www.cnblogs.com/Yellow-ice/p/10433423.html
setTimeout执行问题
https://segmentfault.com/q/1010000009490850
https://segmentfault.com/q/1010000012952958
立即执行函数与异步函数
https://www.cnblogs.com/vickylinj/p/12191958.html
看不懂
https://www.jb51.net/article/188925.htm
变量提升
变量提升，很简单，就是把变量提升提到函数的最top的地方
调用的同名函数是后声明的，函数提升
https://cloud.tencent.com/developer/article/1705113?from=article.detail.1385798
匿名函数与闭包
闭包本身定义比较抽象，MDN官方上解释是：A closure is the combination of a function and the lexical environment within which that function was declared.
闭包是一个函数和该函数被定义时的词法环境的组合
https://www.jianshu.com/p/0a3150afb7ed
js执行顺序
https://www.jianshu.com/p/62c7d633a879
https://segmentfault.com/a/1190000012220307
