[Redux] Using withRouter() to Inject the Params into Connected Components

We will learn how to use withRouter() to inject params provided by React Router into connected components deep in the tree without passing them down all the way down as props.

The app component itself does not really use filter. It just passes the filter down to the visible todo list, which uses it to calculate the currently visible todos. Passing the params from the top level of route handlers gets tedious, so I'm removing the filter prop. Instead, I'm going to find a way to read the current router params in the visible todo list itself.

App.js:

import React from 'react';
import Footer from './Footer';
import AddTodo from './AddTodo';
import VisibleTodoList from './VisibleTodoList';

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

export default App;

I will add a new import code with Router from the React Router package. It's important that we use at least React Router 3.0 for it to work well with Redux. With Router, it takes a React component and returns a different React component that injects the router-related props, such as params, into your component.

//VisibleTodoList.js

import {withRouter} from 'react-router';

I want the params to be available inside mapStateToProps, so I need to wrap the connect result so that the connected component gets the params as a prop. I can scroll up a little bit to the mapStateToProps definition and I can change it so that, rather than read filter directly from ownProps, it's going to read it from ownProps.params.

const mapStateToProps = (state, ownProps) => {
  return {
    todos: getVisibleTodos(state.todos, ownProps.params.filter || 'all'), // if filter is '' then change to 'all'
  };
};

..

const VisibleTodoList = withRouter(connect(
    mapStateToProps,
    mapDispatchToProps
)(TodoList));

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

So instead let router params passed down from the App,  we just let visibleTodoList to get router params by using withRouter. withRouter will inject the params inside router to the props.

import {connect} from 'react-redux';
import {toggleTodo} from '../actions';
import TodoList from './TodoList';
import {withRouter} from 'react-router';

const getVisibleTodos = (todos, filter) => {
    switch (filter) {
        case 'all':
            return todos;
        case 'completed':
            return todos.filter(t => t.completed);
        case 'active':
            return todos.filter(t => !t.completed);
        default:
            throw new Error(`Unknown filter: ${filter}.`);
    }
};

const mapStateToProps = (state, {params}) => {
    return {
        todos: getVisibleTodos(state.todos, params.filter || 'all'), // if filter is '' then change to 'all'
    };
};

const mapDispatchToProps = (dispatch) => {
    return {
        onTodoClick: (id) => {
            dispatch(toggleTodo(id));
        },
    };
};

const VisibleTodoList = withRouter(connect(
    mapStateToProps,
    mapDispatchToProps
)(TodoList));

export default VisibleTodoList;