Throw helpful error when router reducer not mounted under "router"

src/ConnectedRouter.js

@@ -3,9 +3,11 @@ import PropTypes from 'prop-types'
 import { connect } from 'react-redux'
 import { Router } from 'react-router'
 import { onLocationChanged } from './actions'
+import createSelectors from './selectors'
 
 const createConnectedRouter = (structure) => {
-  const { getIn, toJS } = structure
+  const { getIn } = structure
+  const { getRouter, getLocation } = createSelectors(structure)
   /*
    * ConnectedRouter listens to a history object passed from props.
    * When history is changed, it dispatches action to redux store.
@@ -26,7 +28,7 @@ const createConnectedRouter = (structure) => {
           pathname: pathnameInStore,
           search: searchInStore,
           hash: hashInStore,
-        } = toJS(getIn(context.store.getState(), ['router', 'location']))
+        } = getLocation(context.store.getState())
         // Extract history's location
         const {
           pathname: pathnameInHistory,
@@ -102,8 +104,8 @@ const createConnectedRouter = (structure) => {
   }
 
   const mapStateToProps = state => ({
-    action: getIn(state, ['router', 'action']),
-    location: getIn(state, ['router', 'location']),
+    action: getIn(getRouter(state), ['action']),
+    location: getIn(getRouter(state), ['location']),
   })
 
   const mapDispatchToProps = dispatch => ({

src/selectors.js

@@ -2,8 +2,19 @@ import { matchPath } from "react-router"
 
 const createSelectors = (structure) => {
   const { getIn, toJS } = structure
-  const getLocation = state => toJS(getIn(state, ['router', 'location']))
-  const getAction = state => toJS(getIn(state, ['router', 'action']))
+
+  const isRouter = (value) => value != null &&
+    typeof value === 'object' &&
+    getIn(value, ['location']) &&
+    getIn(value, ['action'])
+
+  const getRouter = state => {
+    const router = toJS(getIn(state, ['router']))
+    if (!isRouter(router)) { throw 'Could not find router reducer in state tree, it must be mounted under "router"' }
+    return router
+  }
+  const getLocation = state => toJS(getIn(getRouter(state), ['location']))
+  const getAction = state => toJS(getIn(getRouter(state), ['action']))
 
   // It only makes sense to recalculate the `matchPath` whenever the pathname
   // of the location changes. That's why `createMatchSelector` memoizes
@@ -27,7 +38,7 @@ const createSelectors = (structure) => {
     }
   }
 
-  return {getLocation, getAction, createMatchSelector}
+  return {getLocation, getAction, getRouter, createMatchSelector}
 }
 
 export default createSelectors

test/selectors.test.js

@@ -23,6 +23,36 @@ describe("selectors", () => {
     store = createStore(reducer)
   })
 
+  describe("when router not found under 'router' key", () => {
+    beforeEach(() => {
+      const reducer = combineReducers({
+        notTheRouter: connectRouter(history)
+      })
+      store = createStore(reducer)
+    })
+
+    it("throws helpful error", () => {
+      store.dispatch(push('/'))
+      const state = store.getState()
+      expect(() => getLocation(state)).toThrowError(/^Could not find router reducer in state tree, it must be mounted under "router"$/)
+    })
+  })
+
+  describe("when something else found under 'router' key", () => {
+    beforeEach(() => {
+      const reducer = combineReducers({
+        router: () => ({ some: 'thing' })
+      })
+      store = createStore(reducer)
+    })
+
+    it("throws helpful error", () => {
+      store.dispatch(push('/'))
+      const state = store.getState()
+      expect(() => getLocation(state)).toThrowError(/^Could not find router reducer in state tree, it must be mounted under "router"$/)
+    })
+  })
+
   describe("getLocation", () => {
     it("gets the location from the state", () => {
       const location = { pathname: "/", hash: '', search: '' }