Better fetch module for server-side compat about fbjs

[taion]

@zpao

Webpack prefers the browser version (by default), so it works just fine with isomorphic-fetch and properly pulls in the browser polyfill. I use this exact configuration for my non-Relay applications and it works as expected.

With RN, I believe both versions of the polyfill are set up to not replace the global version if one is already available. The risk would more be if they just completely failed to import - I can't easily test this right now; don't have an RN setup yet.

[taion]

Specifically I use isomorphic-fetch with Webpack in a configuration exactly analogous to the Relay case - isomorphic-fetch is a subdependency of a library that I directly depend on, and Webpack properly resolves the browser version.

[zpao]

Awesome, thanks for the info! Seems like it should just work for the majority of cases then.

With RN, I believe both versions of the polyfill are set up to not replace the global version if one is already available.

You're right it does. Still haven't had a chance to look into the RN support. Perhaps @vjeux knows?

[vjeux]

React Native uses github's fetch implementation that takes over the global variable:
https://github.com/facebook/react-native/blob/7f76f08a11fe1354b132c2875dc2fcf6195c2979/Libraries/Fetch/fetch.js
https://github.com/facebook/react-native/blob/ce814686078058b01bbbf39017745a3ebd1ec07a/Libraries/JavaScriptAppEngine/Initialization/InitializeJavaScriptAppEngine.js#L117-L121

Happy to change it to isomorphic fetch or anything else if it still works in React Native

[taion]

@vjeux: isomorphic-fetch uses keys on package.json to plug into node-fetch or whatwg-fetch. If the RN packager pulls in the browser versions of libraries over the Node versions, then using isomorphic-fetch should just pull in whatwg-fetch. Otherwise there might be some extra work involved.

[zpao]

Talked with @vjeux in person, sounds like the packager will use the browser field so we should be fine. The only issue left for them is then having multiple fetch impls packaged (even if only 1 is used, there are a few extra bytes)

[taion]

Huh? Does the RN packager pull in unused files? Why would it pull in node-fetch at all if it's just going off what's on the browser field?

[zpao]

Didn't say it would. But RN already has a copy of fetch (linked above) so Relay's requires getting rewritten to pull in fbjs/lib/fetch would then bring in a 2nd copy of whatwg-fetch

[taion]

Got it - thanks for explaining that.

[zpao]

The comments in facebook/relay#26 make me think this won't actually work in RN due to self not existing (https://github.com/matthew-andrews/isomorphic-fetch/blob/master/fetch-npm-browserify.js is exactly what we were doing)

[boourns]

@zpao that is correct. I tried this branch with react-native and still ended up with fetch undefined.

[zpao]

I think this got worked out in another PR so going to close out. We'll revisit if we need to.