rxjs裡subscribe和tap的差別

stackoverflow上的讨論：

https://stackoverflow.com/questions/49184754/tap-vs-subscribe-to-set-a-class-property

在tap實作源代碼裡的注釋解釋了tap的用法：

This operator is useful for debugging your Observables for the correct values or performing other side effects.

Note: this is different to a subscribe on the Observable. If the Observable returned by do is not subscribed, the side effects specified by the Observer will never happen. do therefore simply spies on existing execution, it does not trigger an execution to happen like subscribe does.

In general, favor the subscribe block for running side effects, use tap for debugging, but be aware that tap can do more if you need it to.

如果需要編寫具有side effect改變的代碼塊，放在subscribe裡；出于調試目的列印資訊，放在tap裡，但要記住，理論上subscribe能做的，tap也同樣可以。

一位Angular老司機的觀點：

subscribe is ran when the stream is ready for it

so that’s why you have all of the operators in rxjs

so if you have () => {} in your subscribe, then you are waiting for the “final” data

but with tap(), you can do much more work inbetween