Fix react-native fetch

[rodrigobdz]

Importing isomorphic-fetch pollutes the global scope when fetch is already defined. Therefore, check if fetch is defined and dynamically import isomorphic-fetch if not.
PR for #22.

[giannif]

@rodrigobdz this approach works for me. I suggested somewhere (maybe in slack with @cosmocochrane1 ?) just import the ponyfill but I'm not sure where that ended up

[cosmocochrane1]

@giannif Yeah I remember you bringing this up - I did it for the analytics portion. Ill merge this in. @rodrigobdz Thanks!

[giannif]

@cosmocochrane1 ok, if it worked for analytics then we probably should have done it here too, but nbd. If we ever switch to import statements we'll just use the ponyfill

[giannif]

Wait, @cosmocochrane1 @rodrigobdz does this work? We're checking if fetch exists at compile time, no? I'm not familiar with the structure of this project

[rodrigobdz]

@giannif I'm using this solution in my project and it works.

We're checking if fetch exists at compile time, no?

What exactly do you mean by that? Babel does not evaluate the if statement at compile time.
Below is the output of Babel with the if statement as input.

[giannif]

@rodrigobdz, yeah it's fine. I haven't used require in a while and thought for a second that webpack wouldn't bundle the dependency. I've spent all week redoing our chunking in our web app and had that mentality. I'm used to top-level imports and static analysis.

That said, I'm still in favor of the ponyfill approach since this is what they're for

Also, is there any reason why we use require? @cosmocochrane1? Not to go off topic.

[rodrigobdz]

@giannif Using the fetch-ponyfill instead sounds good. isomorphic-fetch is no longer maintained.