init

Author: darthmaim

.gitignore

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+node_modules
+lib

LICENSE

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+MIT License
+
+Copyright (c) 2017 darthmaim
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

README.md

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+# redux-sync-reducer
+
+High order reducer to sync states between tabs.
+
+## Installation
+
+```
+npm install --save redux-sync-reducer
+```
+
+## Usage
+
+Wrap the reducers you want synced between tabs with `syncedReducer`.
+
+```js
+import { syncedReducer } from 'redux-sync-reducer';
+
+syncedReduer(reducer);
+```
+
+You also need to add the `syncMiddleware` when creating your store. 
+This middleware will dispatch actions when the synced state gets changed in another tab.
+
+```js
+import { syncMiddleware } from 'redux-sync-reducer';
+
+const store = createStore(reducers, applyMiddleware(syncMiddleware));
+```
+
+## API
+
+```js
+import { syncedReducer } from 'redux-sync-reducer';
+syncedReducer(reducer)
+syncedReducer(reducer, config)
+```
+
+## Config
+
+You can pass a config object to `syncedReducer`.
+
+option          | default     | description
+--------------- | ----------- | ------------
+**name**        | `reducer.toString()` | Pass a custom name for the reducer.<br>See [why you might need this](#When-using-multiple-different-syncedReducers-all-receive-the-same-state).
+**skipReducer** | `false` | When the internal action is dispatched, it will call your own reducer with the new value. You can skip this by setting `skipReducer` to `true`.
+
+## Common issues
+
+### When using multiple different `syncedReducers` all receive the same state
+
+You are probably wrapping your reducers in another high order reducer (for example `handleAction` from `redux-actions`) before passing it to `syncedReducer`. `syncedReducer` can't distinguish between the different reducers and you have to set a custom
+name when creating it.
+
+```js
+export const counter = syncedReducer(handleAction(INCREASE, state => state + 1, { name: 'counter' }));
+```
+
+## License
+
+**redux-sync-reducer** is licensed under the [MIT License](LICENSE).

package.json

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+{
+  "name": "redux-sync-reducer",
+  "version": "0.0.1",
+  "description": "High order reducer to sync partial states between tabs",
+  "main": "lib/index.js",
+  "scripts": {
+    "test": "echo \"Error: no test specified\" && exit 1",
+    "clean": "rimraf lib",
+    "build": "BABEL_ENV=commonjs babel src --out-dir lib",
+    "prepublish": "npm run clean && npm run build"
+  },
+  "repository": {
+    "type": "git",
+    "url": "https://github.com/darthmaim/redux-sync-reducer.git"
+  },
+  "keywords": [
+    "redux",
+    "sync"
+  ],
+  "author": "darthmaim",
+  "license": "MIT",
+  "bugs": {
+    "url": "https://github.com/darthmaim/redux-sync-reducer/issues"
+  },
+  "homepage": "https://github.com/darthmaim/redux-sync-reducer#readme",
+  "devDependencies": {
+    "babel-cli": "^6.24.0",
+    "babel-preset-es2015": "^6.24.0",
+    "rimraf": "^2.6.1"
+  },
+  "babel": {
+    "presets": [
+      "es2015"
+    ]
+  }
+}

src/index.js

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+/** 
+ * Checks if localStorage is supported.
+ * @constant
+ * @type {Boolean}
+ */
+const isSupported = !!(window && window.localStorage);
+
+/**
+ * List of all reducer names that are synced.
+ * @type {string[]}
+ */
+const syncedReducers = [];
+
+
+/**
+ * Get the type of the action.
+ * @param {string} name 
+ */
+function getActionType(name) {
+    return `@@sync-reducer/sync/${name}`;
+}
+
+/**
+ * Get the key used in localStorage.
+ */
+function getKeyName(name) {
+    return `@@sync-reducer/${name}`;
+}
+
+/**
+ * Sync data between tabs.
+ * @param {string} name 
+ * @param {object} data 
+ */
+function sync(name, data) {
+    if(isSupported) {
+        window.localStorage.setItem(getKeyName(name), JSON.stringify(data));
+    }
+
+    return data;
+}
+
+/**
+ * High level reducer to wrap reducers to sync the state between tabs.
+ * @param {function} reducer 
+ * @param {object} config 
+ */
+export function syncedReducer(reducer, config = {}) {
+    const name = config.name || reducer.toString();
+    const actionType = getActionType(name);
+
+    syncedReducers.push(name);
+
+    return (state, action = {}, ...slices) => {
+        switch(action.type) {
+            case actionType:
+                return config.skipReducer ? action.payload : reducer(action.payload, action, ...slices);
+            default:
+                return sync(name, reducer(state, action, ...slices));
+        }
+    }
+}
+
+/**
+ * Registers storage event listener and dispatches actions when the state gets changed in different tabs.
+ */
+export const syncMiddleware = store => {
+    isSupported && window.addEventListener('storage', e => {
+        syncedReducers.some(name => {
+            if(e.key === getKeyName(name)) {
+                store.dispatch({
+                    type: getActionType(name),
+                    payload: JSON.parse(e.newValue)
+                });
+
+                return true;
+            }
+
+            return false;
+        })
+    });
+
+    return next => action => next(action);
+}