add combine-reducers

.babelrc

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+{
+  "presets": [
+      "env"
+  ]
+}

.gitignore

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+node_modules/
+coverage/

package.json

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+{
+  "name": "combine-reducers",
+  "version": "1.0.0",
+  "main": "src/combine-reducers.js",
+  "license": "MIT",
+  "scripts": {
+    "test": "jest",
+    "build": "webpack"
+  },
+  "devDependencies": {
+    "babel": "^6.23.0",
+    "babel-loader": "^7.1.2",
+    "babel-preset-env": "^1.6.1",
+    "jest": "^22.1.4",
+    "uglifyjs-webpack-plugin": "^1.1.6",
+    "webpack": "^3.10.0"
+  }
+}

readme.md

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+# combine-reducers
+
+a standalone ES6 combine-reducers function. Unit tested. Babel pre-configured.
+
+```
+yarn run v1.3.2
+$ jest --coverage
+ PASS  test/combine-reducers.test.js
+  combineReducers
+    ✓ should add a customer and a pony into eachs state (3ms)
+
+Test Suites: 1 passed, 1 total
+Tests:       1 passed, 1 total
+Snapshots:   0 total
+Time:        0.895s, estimated 1s
+Ran all test suites.
+---------------------|----------|----------|----------|----------|----------------|
+File                 |  % Stmts | % Branch |  % Funcs |  % Lines |Uncovered Lines |
+---------------------|----------|----------|----------|----------|----------------|
+All files            |      100 |        0 |      100 |      100 |                |
+ combine-reducers.js |      100 |        0 |      100 |      100 |              1 |
+---------------------|----------|----------|----------|----------|----------------|
+✨  Done in 1.88s.
+```

src/combine-reducers.js

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+export default (reducers = {}) => (state = {}, action) => 
+	Object.assign(
+		{},
+		state,
+		...Object.keys(reducers).map(key => ({
+			[key]: reducers[key](state[key], action)
+		})
+	))

test/combine-reducers.test.js

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+import combineReducers from '../src/combine-reducers'
+
+const reducerCustomers = (state = [], action) => action.type === 'SET_CUSTOMER' ? {
+	customer: action.customer
+} : state
+const reducerPonys = (state = [], action) => action.type === 'SET_PONY' ? {
+	pony: action.pony
+} : state
+
+describe('combineReducers', () => {
+	it('should add a customer and a pony into eachs state', () =>{
+		const customer = {name: `customer-${Math.random(100)}`}
+		const pony = {name: `pony-${Math.random(100)}`}
+
+		const combinedReducers = combineReducers({
+			reducerCustomers,
+			reducerPonys
+		});
+
+		const firstState = combinedReducers({}, { type: 'SET_CUSTOMER', customer })
+		expect(firstState.reducerCustomers.customer).toEqual(customer)
+
+		const secondState = combinedReducers(firstState, { type: 'SET_PONY', pony })
+		expect(secondState.reducerPonys.pony).toEqual(pony)
+	})
+})

webpack.config.js

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+const path = require('path');
+const UglifyJsPlugin = require('uglifyjs-webpack-plugin')
+
+module.exports = {
+  entry: './src/combine-reducers.js',
+  output: {
+    filename: 'bundle.js',
+    path: path.resolve(__dirname, 'dist')
+  },
+  module: {
+    loaders: [
+      {
+        test: /\.js$/,
+        loader: 'babel-loader',
+        query: {
+            presets: ['env']
+        }
+      }
+    ]
+  },
+  stats: {
+      colors: true
+  },
+  devtool: 'source-map',
+  plugins: [
+    new UglifyJsPlugin()
+  ]
+};