为什么

const a1 = [1, 2]

a1 instanceof Object // true 
a1 instanceof Array // true

答案：

a1.__proto__.constructor === Array // true
a1.__proto__.constructor === Object // false

缓存：

缓存的分类

1. 强缓存 Expires Expires:Thu, 21 Jan 2017 23:39:02 GMT Cache-Control Cache-Control:max-age=3600
2. 协商缓存 Last-Modified If-Modified-Since Last-Modified: Wed, 26 Jan 2017 00:35:11 GMT Etag If-None-Match

https://segmentfault.com/a/1190000040748678