# redux-subscriber

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This package allows you to subscribe to changes in any part of [Redux](https://github.com/reactjs/redux) state.

## Installation

`npm install redux-subscriber --save`

## Usage

_store.js_
```js
import {createStore} from 'redux';
import initSubscriber from 'redux-subscriber';

const store = createStore(...);

// "initSubscriber" returns "subscribe" function, so you can use it
const subscribe = initSubscriber(store);
```

_somewhere-else.js_
```js
// or you can just import "subscribe" function from the package
import {subscribe} from 'redux-subscriber';

const unsubscribe = subscribe('user.messages.count', state => {
    // do something
});

// if you want to stop listening to changes
unsubscribe();

```

## Examples

* https://github.com/ivantsov/yandex-mail-notifier-chrome - real app that uses `redux-subscriber`

## API

#### `initSubscriber(store)` (_default export_) - initialize `redux-subscriber`, so after that you can use `subscribe` method.

#### Options

- `store` - instance of Redux store.

Returns `subscribe` function.

#### `subscribe(key, callbackFunction)` - subscribe `callbackFunction` to changes.

#### Options

- `key` - string which specified the part of state (e.g. `user.message.count`) to listen to. 
- `callbackFunction` - function which will be called when the part of state has changed. New state is passed as a parameter.

Returns `unsubscribe` function which can be called to unsubscribe from changes.