Hope be much frendly to setup custom API

It's hard to setup custom with current package, because the is no development model , such as  code watch , debugger env and any auxiliary  tools, and did not even report an error (
Maybe the method I tried has a problem ).

For example, if I want to setup custom API base on  match  the React 16 , I will feel that I can't start.

So, I am curious about how you setup custom API base React 15 ?