metamask-extension/ui/app/store/store.js

const createStore = require('redux').createStore
const applyMiddleware = require('redux').applyMiddleware
const thunkMiddleware = require('redux-thunk').default
const rootReducer = require('../ducks')
const createLogger = require('redux-logger').createLogger

global.METAMASK_DEBUG = process.env.METAMASK_DEBUG

module.exports = configureStore

const loggerMiddleware = createLogger({
  predicate: () => global.METAMASK_DEBUG,
})

const middlewares = [thunkMiddleware, loggerMiddleware]

const createStoreWithMiddleware = applyMiddleware(...middlewares)(createStore)

function configureStore (initialState) {
  return createStoreWithMiddleware(rootReducer, initialState)
}