[Redux] Generating Containers with connect() from React Redux (AddTodo)

Code to be refacted:

const AddTodo = (props, { store }) => {
  let input;

  return (
    <div>
      <input ref={node => {
        input = node;
      }} />
      <button onClick={() => {
        store.dispatch({
          type: 'ADD_TODO',
          id: nextTodoId++,
          text: input.value
        })
        input.value = '';
      }}>
        Add Todo
      </button>
    </div>
  );
};
AddTodo.contextTypes = {
  store: React.PropTypes.object
};

Instead of passing:

const AddTodo = (props, { store }) => {

We can only pass 'props', and we get 'dispatch' from the props:

let AddTodo = ({ dispatch }) => {

Then we will create a container component with connect that will inject that the dispatch function as a prop, we will remove the context types because the component generated by connect function will take care of reading this chore from the context.

The first argument to the connect function is map straight to props, but there aren't any props for at to-do component that depend on the current state, so I return an empty object. The second argument to connect is map dispatch to props, but at to-do component doesn't need any callback props. It just accepts the dispatch function itself, so I'm returning it as a prop with the same name.

Finally, I'm calling the function for a second time to specify the component I want to wrap, in this case, AddTodo itself:

AddTodo = connect(
  state => {
    return {};
  },
  dispatch => {
    return {dispatch};
  }
)(AddTodo);

However, it is wasteful to even subscribe to this chore if we don't calculate any props from its state. So I'm replacing the mapStateToProps function with an null, which tells connect that there is no need to subscribe to this store.

Additionally, it's pretty common pattern to inject just the dispatch function. This is why if you specify null or any false value in connect as the second argument, you're going to get dispatch injected as a prop. 

AddTodo = connect(
  null,
  null
)(AddTodo);

In fact, I can just remove all arguments here. The default behavior will be to not subscribe to this chore and to inject just the dispatch function as a prop.:

AddTodo = connect()(AddTodo);

So the AddTodo function would looks like:

let AddTodo = ({ dispatch }) => {
  let input;

  return (
    <div>
      <input ref={node => {
        input = node;
      }} />
      <button onClick={() => {
        dispatch({
          type: 'ADD_TODO',
          id: nextTodoId++,
          text: input.value
        })
        input.value = '';
      }}>
        Add Todo
      </button>
    </div>
  );
};
AddTodo = connect()(AddTodo);

The AddTodo component that I declare accepts dispatch as a prop, but it doesn't know how to get this store. It just hopes that someone is going to pass the dispatch to it.

The connect code without any arguments is going to generate a container component that does not subscribe to this store. However, that will pass dispatch to the component that it wraps. In this case, it wraps my AddTodo component.

The second connect call returns the generated container component. I'm assigning it to AddTodo. I'm reassigning the let binding the second time.

------------------

Code:

const todo = (state, action) => {
  switch (action.type) {
    case 'ADD_TODO':
      return {
        id: action.id,
        text: action.text,
        completed: false
      };
    case 'TOGGLE_TODO':
      if (state.id !== action.id) {
        return state;
      }

      return {
        ...state,
        completed: !state.completed
      };
    default:
      return state;
  }
};

const todos = (state = [], action) => {
  switch (action.type) {
    case 'ADD_TODO':
      return [
        ...state,
        todo(undefined, action)
      ];
    case 'TOGGLE_TODO':
      return state.map(t =>
        todo(t, action)
      );
    default:
      return state;
  }
};

const visibilityFilter = (
  state = 'SHOW_ALL',
  action
) => {
  switch (action.type) {
    case 'SET_VISIBILITY_FILTER':
      return action.filter;
    default:
      return state;
  }
};

const { combineReducers } = Redux;
const todoApp = combineReducers({
  todos,
  visibilityFilter
});

const { Component } = React;

const Link = ({
  active,
  children,
  onClick
}) => {
  if (active) {
    return <span>{children}</span>;
  }

  return (
    <a href='#'
       onClick={e => {
         e.preventDefault();
         onClick();
       }}
    >
      {children}
    </a>
  );
};

class FilterLink extends Component {
  componentDidMount() {
    const { store } = this.context;
    this.unsubscribe = store.subscribe(() =>
      this.forceUpdate()
    );
  }
  
  componentWillUnmount() {
    this.unsubscribe();
  }
  
  render() {
    const props = this.props;
    const { store } = this.context;
    const state = store.getState();
    
    return (
      <Link
        active={
          props.filter ===
          state.visibilityFilter
        }
        onClick={() =>
          store.dispatch({
            type: 'SET_VISIBILITY_FILTER',
            filter: props.filter
          })
        }
      >
        {props.children}
      </Link>
    );
  }
}
FilterLink.contextTypes = {
  store: React.PropTypes.object
};

const Footer = () => (
  <p>
    Show:
    {' '}
    <FilterLink filter='SHOW_ALL'>
      All
    </FilterLink>
    {', '}
    <FilterLink filter='SHOW_ACTIVE'>
      Active
    </FilterLink>
    {', '}
    <FilterLink filter='SHOW_COMPLETED'>
      Completed
    </FilterLink>
  </p>
);

const Todo = ({
  onClick,
  completed,
  text
}) => (
  <li
    onClick={onClick}
    style={{
      textDecoration:
        completed ?
          'line-through' :
          'none'
    }}
  >
    {text}
  </li>
);

const TodoList = ({
  todos,
  onTodoClick
}) => (
  <ul>
    {todos.map(todo =>
      <Todo
        key={todo.id}
        {...todo}
        onClick={() => onTodoClick(todo.id)}
      />
    )}
  </ul>
);

const { connect } = ReactRedux;

let nextTodoId = 0;
let AddTodo = ({ dispatch }) => {
  let input;

  return (
    <div>
      <input ref={node => {
        input = node;
      }} />
      <button onClick={() => {
        dispatch({
          type: 'ADD_TODO',
          id: nextTodoId++,
          text: input.value
        })
        input.value = '';
      }}>
        Add Todo
      </button>
    </div>
  );
};
AddTodo = connect()(AddTodo);

const getVisibleTodos = (
  todos,
  filter
) => {
  switch (filter) {
    case 'SHOW_ALL':
      return todos;
    case 'SHOW_COMPLETED':
      return todos.filter(
        t => t.completed
      );
    case 'SHOW_ACTIVE':
      return todos.filter(
        t => !t.completed
      );
  }
}

const mapStateToTodoListProps = (state) => {
  return {
    todos: getVisibleTodos(
      state.todos,
      state.visibilityFilter
    )
  };
};

const mapDispatchToTodoListProps = (dispatch) => {
  return {
    onTodoClick: (id) => {
      dispatch({
        type: 'TOGGLE_TODO',
        id
      });
    }
  };
};


const VisibleTodoList = connect(
  mapStateToTodoListProps,
  mapDispatchToTodoListProps
)(TodoList);

const TodoApp = () => (
  <div>
    <AddTodo />
    <VisibleTodoList />
    <Footer />
  </div>
);

const { Provider } = ReactRedux;
const { createStore } = Redux;

ReactDOM.render(
  <Provider store={createStore(todoApp)}>
    <TodoApp />
  </Provider>,
  document.getElementById('root')
);