# Step 2.7: Connect Redux store to view (Demo)

[Lessons](../) | [Exercise](./exercise/) | [Demo](./demo/)

Redux is currently the most popular Flux implementation, and the ecosystem of related libraries has grown as a result. This is one of the reasons why it is a very popular library within Microsoft products.

Various GitHub users have collected "awesome lists" of tech and articles related to Redux. Here is [one such list](https://github.com/xgrommx/awesome-redux#react---a-javascript-library-for-building-user-interfaces), but it is literally impossible to list out all the related tech.

In this step, we introduce but one useful library that works with Redux: [`react-redux`](https://react-redux.js.org/).

## The official React Redux binding: `react-redux`

That's right, Redux doesn't just work with React. It can also be used with Vue.js, Angular, and React Native, to name a few.

### `<Provider>` component

The store doesn't magically get passed to the views. It has to be supplied by a `react-redux` component called [`<Provider>`](https://react-redux.js.org/api/provider). A `<Provider>` can be placed anywhere, but it's best to just make it available at the root the app:

```js
const store = createStore(reducers);

const App = () => {
  return (
    <Provider store={store}>
      <div>Hello World!</div>
    </Provider>
  );
};
```

### `connect()` higher-order function

`react-redux` provides a [`connect()`](https://react-redux.js.org/api/connect) function that turns the Redux store and dispatch functions into props for React components. The state and action dispatchers are passed along with a `<Provider>` component.

```js
const OldComponent = props => {
  return <div>{props.foo}</div>;
};

const NewComponent = connect(
  mapStateToProps,
  mapDispatchToProps,
  mergeProps,
  options
)(OldComponent);
```

`connect()` takes in a few functions that map portions of the state tree and dispatcher functions into props. It is a **higher-order function**, meaning that the return value of `connect()` is a function that decorates `OldComponent` into a `NewComponent` with all the mapped props.

Next we'll learn about how to write `mapStateToProps` and `mapDispatchToProps`. For demonstration purposes, we'll assume the store and the component props look like this:

```ts
interface Store {
  foo: string;
  // and probably some other properties
}

interface ComponentProps {
  foo: string;
  addTodo: (label: string) => void;
}
```

#### `mapStateToProps`

A [`mapStateToProps`](https://react-redux.js.org/api/connect#mapstatetoprops-state-ownprops-object) function uses the state tree as a parameter and selects portions of it that will be passed to the component as part of `props`. When values in the state tree change, the `mapStateToProps` function is called, and the new props are passed to the component (causing React to re-render it).

```ts
function mapStateToProps(state: Store): Partial<ComponentProps> {
  return {
    foo: state.foo
  };
}
```

#### `mapDispatchToProps`

A [`mapDispatchToProps`](https://react-redux.js.org/api/connect#mapdispatchtoprops-object-dispatch-ownprops-object) function generates props which are used to dispatch Redux actions. This function generally returns props which the component will use as callbacks in response to user actions.

```ts
function mapDispatchToProps(dispatch: any): Partial<ComponentProps> {
  return {
    // the dispatched message COULD be generated by an
    // action creator instead (see later steps)
    addTodo: (label: string) => dispatch({ type: 'addTodo', label })
  }
}
```