But in spite of all these tendencies, Scientific Pedagogy has never yet been definitely constructed nor defined. It is something vague of which we speak, but which does not,[Pg 2] in reality, exist. We might say that it has been, up to the present time, the mere intuition or suggestion of a science which, by the aid of the positive and experimental sciences that have renewed the thought of the nineteenth century, must emerge from the mist and clouds that have surrounded it.

What if MobX did make assumptions on how your data is structured? What if it is opinionated? That is the curious case of Mobx state tree.

const list = [].concat(x);

在过期时间前，资源缓存是有效的，反之则缓存失效。通过不停抛弃过期的缓存资源以保证资源的实时性。注意，旧的缓存不会被抛弃或者忽略；当发起一个针对旧缓存资源的请求时，会在请求头里带上If-None-Match用来判断缓存是否还有效。如果有效，服务端返回304(Not Modified)和空的body以节省一部分带宽。

only wish I had your course a long time ago; it would have saved me years of slow progress.