learn-co-students/map-state-to-props-lab-london-web-111918

Mapping State to Props Using React and Redux

Objectives

• Use the React Redux library to connect the store to the React application.

• Utilize the <Provider /> component, the connect function and mapStateToProps to access Redux store content.

Overview

In this lesson, we want to explore how mapStateToProps is used to connect regular React components with the Redux store. This is also a good opportunity to review the steps for using the redux and react-redux packages in your app.

Instructions

Some files are provided, including UserInput and the reducer, manageUsers, but the Redux store isn't fully hooked up yet.

Connecting to Redux

In src/index.js, use the createStore method from redux, passing in the provided reducer, manageUsers, to create a store. Use Provider from react-redux to wrap <App />, passing store as a prop to the Provider. This will give your components access to the store.

Test by Dispatching an Action

Run npm start and open up your browser's dev console. If everything is connected correctly in index.js, a form should appear in the browser. Submitting something using the form will cause a console.log to fire in our reducer, indicating that the values have been added to our store.

In UserInput.js, we can see the code that fires when we press the submit button:

...

handleOnSubmit = (event) => {
  event.preventDefault();
  this.props.dispatch({type: 'ADD_USER', user: this.state})
}

render() {
  return(
    <form onSubmit={this.handleOnSubmit}>
      ...
    </form>
  )
}

We can see that, on submit, handleOnSubmit() is called. event.preventDefault() is called to stop the page from refreshing, then this.props.dispatch() is called with a custom action, {type: 'ADD_USER', user: this.state}.

export default connect()(UserInput);

Wrapping a component in connect as we see above will, by default, pass one function to props: dispatch(). This makes it possible for us to dispatch custom actions, as we see here in handleOnSubmit().

We will go into greater detail on how we can customize our dispatches using connect, but using this.props.dispatch() like this is a handy way to allow any component to interact with the store.

Mapping State

Now that we've got a working store, we want to get access to it and display the contents of our store's state.

1. Connect the Users component similar to how it is connected in UserInput.

2. Write a function in Users.js, but outside of the Users class, called mapStateToProps. mapStateToProps accepts one argument, state, the current version of your store's state. Use state to access the array of users. Your mapStateToProps function should return an object with keys. Each key will become a prop in your component, allowing you to assign values based on the provided state.

The Users component should display the username of a user submitted to the store. To pass the final test, it should also display a total count of current users. Try to use mapStateToProps to solve both, returning two keys, one for users and one for the userCount.

Conclusion

With all tests passing, you should have a working form that adds and successfully displays usernames, as well as a total count of those users. While these are small bits of data, we've got a fully integrated React/Redux application, ready to be expanded upon!