how does flow work?

flow must work with babel-core this whole project is writting in es6 syntax (destruction assignmnet, spread and rest, class property transform... all es6 features) we just not using import/export but rather require instead in favor of flow syntax

for a normal react project

npm ls babel-preset-flow
D:\learn-relay\relay-modern
`-- babel-preset-react@6.24.1
  `-- babel-preset-flow@6.23.0

for react-relay (which is also a react1 application, but deeply customized)

$ npm ls | grep flow
+-- babel-plugin-transform-flow-strip-types@6.22.0
| `-- babel-plugin-syntax-flow@6.18.0
+-- eslint-plugin-flowtype@2.30.4
+-- flow-bin@0.46.0 invalid

a healthy flow output

terminal flow on centOS works fine. on windows git-bash, the behavior is a bit unpredictable (keeps restarting ..etc)

$ flow status --no-auto-start  --json
{"flowVersion":"0.46.0","errors":[],"passed":true}

flow output

[2017-05-26T03:05:53.646Z] [INFO] flow - Path to Flow: flow
[2017-05-26T03:05:53.714Z] [INFO] flow - [unknown]: Flow server in d:\relay-modern
[2017-05-26T03:05:53.962Z] [INFO] flow - [ready]: Flow server in d:\relay-modern
[2017-05-26T03:05:55.451Z] [INFO] flow - [not running]: Flow server in d:\relay-modern
[2017-05-26T03:05:55.734Z] [INFO] flow - [init]: Flow server in d:\relay-modern
[2017-05-26T03:06:10.390Z] [INFO] flow - [ready]: Flow server in d:\relay-modern

1. each fragment instance (containers) has a FragmentSpecResolver which is of type RelayModernFragmentSpecResolver
2. RelayModernFragmentSpecResolver has a list of selector resolvers, which are of type SelectorResolver

class SelectorResolver {
    this._data = snapshot.data;  // it has data
    this._selector = selector;   // and it knoww how to fetch data from MarkSeepStore
}    

3. a selector is