feat: allow to use Record and other Iterables as default state value (#58)

* fix: correct test glob pattern

* feat: allow using custom default state

* test: add tests for custom default state

* docs: update README with custom default state usage

Author: Velenir

README.md

@@ -37,6 +37,29 @@ const rootReducer = combineReducers({});
 const store = createStore(rootReducer, initialState);
 ```
 
+By default, if `state` is `undefined`, `rootReducer(state, action)` is called with `state = Immutable.Map()`. A different default function can be provided as the second parameter to `combineReducers(reducers, getDefaultState)`, for example:
+
+```js
+const StateRecord = Immutable.Record({
+	foo: 'bar'
+});
+const rootReducer = combineReducers({foo: fooReducer}, StateRecord);
+// rootReducer now has signature of rootReducer(state = StateRecord(), action)
+// state now must always have 'foo' property with 'bar' as its default value
+```
+
+When using `Immutable.Record` it is possible to delegate default values to child reducers:
+
+```js
+const StateRecord = Immutable.Record({
+	foo: undefined
+});
+const rootReducer = combineReducers({foo: fooReducer}, StateRecord);
+// state now must always have 'foo' property with its default value returned from fooReducer(undefined, action)
+```
+
+In general, `getDefaultState` function must return an instance of `Immutable.Iterable` that implements `get`, `set` and `withMutations` methods. Such iterables are `List`, `Map`, `OrderedMap` and `Record`.
+
 ### Using with `react-router-redux`
 
 `react-router-redux` [`routeReducer`](https://github.com/reactjs/react-router-redux/tree/v4.0.2#routerreducer) does not work with Immutable.js. You need to use a custom reducer:

package.json

@@ -40,7 +40,7 @@
   },
   "scripts": {
     "lint": "eslint ./src ./tests",
-    "test": "mocha --compilers js:babel-register ./tests/**/*.js",
+    "test": "mocha --compilers js:babel-register './tests/**/*.js'",
     "build": "babel ./src --source-maps --out-dir ./dist",
     "benchmark": "NODE_ENV=production node ./benchmarks/index.js",
     "precommit": "npm run lint && npm run test"

src/combineReducers.js

@@ -4,11 +4,11 @@ import {
   validateNextState
 } from './utilities';
 
-export default (reducers: Object): Function => {
+export default (reducers: Object, getDefaultState: ?Function = Immutable.Map): Function => {
   const reducerKeys = Object.keys(reducers);
 
   // eslint-disable-next-line space-infix-ops
-  return (inputState: ?Immutable.Map = Immutable.Map(), action: Object): Immutable.Map => {
+  return (inputState: ?Function = getDefaultState(), action: Object): Immutable.Map => {
     // eslint-disable-next-line no-process-env
     if (process.env.NODE_ENV !== 'production') {
       const warningMessage = getUnexpectedInvocationParameterMessage(inputState, reducers, action);

tests/combineReducers.js

@@ -65,8 +65,98 @@ describe('combineReducers()', () => {
         })
       });
 
-            // eslint-disable-next-line no-undefined
+      // eslint-disable-next-line no-undefined
       expect(rootReducer(undefined, {})).to.eql(initialState);
     });
   });
+  context('root reducer uses a custom Immutable.Iterable as default state', () => {
+    it('returns initial state as instance of supplied Immutable.Record', () => {
+      const defaultRecord = Immutable.Record({
+        bar: {
+          prop: 1
+        },
+        foo: undefined  // eslint-disable-line no-undefined
+      });
+      const rootReducer = combineReducers({
+        bar: (state) => {
+          return state;
+        },
+        foo: (state = {count: 0}) => {
+          return state;
+        }
+      }, defaultRecord);
+
+      const initialState = {
+        bar: {
+          prop: 1
+        },
+        foo: {
+          count: 0
+        }
+      };
+
+      // eslint-disable-next-line no-undefined
+      const reducedState = rootReducer(undefined, {});
+
+      expect(reducedState.toJS()).to.deep.equal(initialState);
+      expect(reducedState).to.be.instanceof(defaultRecord);
+    });
+    it('returns initial state as instance of Immutable.OrderedMap', () => {
+      const rootReducer = combineReducers({
+        bar: (state = {prop: 1}) => {
+          return state;
+        },
+        foo: (state = {count: 0}) => {
+          return state;
+        }
+      }, Immutable.OrderedMap);
+
+      const initialState = {
+        bar: {
+          prop: 1
+        },
+        foo: {
+          count: 0
+        }
+      };
+
+      // eslint-disable-next-line no-undefined
+      const reducedState = rootReducer(undefined, {});
+
+      expect(reducedState.toJS()).to.deep.equal(initialState);
+      expect(reducedState).to.be.instanceof(Immutable.OrderedMap);
+    });
+    it('returns initial state as result of custom function call', () => {
+      const getDefaultState = () => {
+        return Immutable.Map({
+          bar: {
+            prop: 1
+          }
+        });
+      };
+      const rootReducer = combineReducers({
+        bar: (state) => {
+          return state;
+        },
+        foo: (state = {count: 0}) => {
+          return state;
+        }
+      }, getDefaultState);
+
+      const initialState = {
+        bar: {
+          prop: 1
+        },
+        foo: {
+          count: 0
+        }
+      };
+
+      // eslint-disable-next-line no-undefined
+      const reducedState = rootReducer(undefined, {});
+
+      expect(reducedState.toJS()).to.deep.equal(initialState);
+      expect(reducedState).to.be.instanceof(Immutable.Map);
+    });
+  });
 });