Introduction to React Router

Objectives

Describe React Router's approach to client-side routing
Explain how React Router allows building a route tree as a component
Describe how routes are matched in React Router

A complicated world needs an address

So far, we have been building our applications without any navigation, so everything in the app has lived at the same URL. Currently, we can make it look like we are changing the page, by showing or hiding some components, but none of these changes are dependent on a change in the URL.

Now this may seem like a small quibble, but web addresses are the backbone of the Internet. The web is just a series of links to other pages, after all. Let's imagine that we have a React application hosted at www.loveforsoils.com (not a real website) dedicated to sharing knowledge about soil types. As a facet of our React application, we want to provide users with the option to see a list of our favorite soils. Currently, instead of sharing a link to a list of our favorite soils, we can only provide a link to our "Love for soils" homepage. Following which, users are required to interact with our application to see a favorite soil list.

Because our personal opinion on the best soils is so important, we want to provide users with the opportunity to go straight to this list of the favorite soils view with a URL. Enter React Router: a routing library for React that allows us to link to specific URLs then show or hide various components depending on which URL is displayed. As React Router's documentation states:

Components are the heart of React's powerful, declarative programming model. React Router is a collection of navigational components that compose declaratively with your application. Whether you want to have bookmarkable URLs for your web app or a composable way to navigate in React Native, React Router works wherever React is rendering--so take your pick!

For this README we will be building our first Component routes as a code along.

Code Along

Setting up our Main Route

Note: Make sure you clone down this repo, run npm install && npm start, and open http://localhost:3000 in the browser.

If you open up src/index.js, you will see that currently we are defining a Home component, and then rendering that component in the DOM.

// ./src/index.js

import React from 'react';
import ReactDOM from 'react-dom';

const Home = () => {
  return (
    <div>
      <h1>Home!</h1>
    </div>
  );
};

ReactDOM.render(
  <Home />,
  document.getElementById('root')
);

With React Router our core routing will live in this component. We will define our various routes within this file. To start using routes, we need to install react-router-dom:

npm install react-router-dom

To start implementing routes, we first need to import BrowserRouter and Route from react-router-dom. BrowserRouter is commonly renamed as Router, so we'll follow this convention, as well. We can create an alias with the syntax BrowserRouter as Router. So every time we refer to Router, in this file, we are really just refering to BrowserRouter.

// .src/index.js

import React from 'react';
import ReactDOM from 'react-dom';
// Step 1. Import react-router functions
import { BrowserRouter as Router, Route } from 'react-router-dom';

const Home = () => {
  return (
    <div>
      <h1>Home!</h1>
    </div>
  );
};

// Step 2. Changed to have router coordinate what is displayed
ReactDOM.render((
  <Router>
    <Route path="/" component={Home} />
  </Router>),
  document.getElementById('root')
);

Step 1: In Step 1 above, there are two components that we are importing from React Router. We use them in turn.

Step 2: The Router (our alias for BrowserRouter) component is the base for our application's routing. It is where we declare how React Router will be used. Notice that nested inside the Router component we use the Route component. The Route component has two props in our example: path and component. The Route component is in charge of saying: "when the URL matches this specified path, render this specified component".

Let's try it. Copy the above code into src/index.js and run npm start to boot up the application. Once it is running, point your URL to http://localhost:3000/. What you'll notice is that when you type in the URL it will render a <div><h1>Home!</h1></div>.

Adding Additional Routes

In the last two steps, we learned how to set up the basic Router component and inject our very first Route component.

Next, we want to add components for About and Login:

// ./src/index.js
import React from 'react';
import ReactDOM from 'react-dom';
import { BrowserRouter as Router, Route } from 'react-router-dom';

const Home = () => {
  return (
    <div>
      <h1>Home!</h1>
    </div>
  );
};

const About = () => {
  return (
    <div>
      <h1>This is my about component!</h1>
    </div>
  );
};

const Login = () => {
  return (
    <div>
      <form>
        <div>
          <input type="text" name="username" placeholder="Username" />
          <label htmlFor="username">Username</label>
        </div>
        <div>
          <input type="password" name="password" placeholder="Password" />
          <label htmlFor="password">Password</label>
        </div>
        <input type="submit" value="Login" />
      </form>
    </div>
  );
};

Following, let's add our /about and /login routes to our router:

// ./src/index.js

ReactDOM.render((
  <Router>
      <Route path="/" component={Home} />
      <Route exact path="/about" component={About} />
      <Route exact path="/login" component={Login} />
  </Router>),
  document.getElementById('root')
);

Reload your browser and look at our beautiful routes...oops! Error:

A <Router> may have only one child element

If you open up your browser dev tools console you should be seeing the same error. What does this mean? Well, as you know in React, a component must return one child/html node (which may wrap many others). We just gave Router three children! To remedy this problem we can place all of the Route components into a <div> tag:

ReactDOM.render((
  <Router>
    <div>
      <Route path="/" component={Home} />
      <Route exact path="/about" component={About} />
      <Route exact path="/login" component={Login} />
    </div>
  </Router>),
  document.getElementById('root')
);

Let's go back to the browser and assert that our application is back to functioning. We see that our Home component is displaying. Try manually typing in the URL locations for /, /about, and /login. Do you see the other components rendering?

You may have noticed the aberrant behavior of the Home component. It is always rendering, no matter which route we go to! Even if we type in nonsense following the /, we still get the Home component.

Imagine we had a header we wanted displayed no matter which route was hit. In that case, this behavior is desirable! Otherwise, there are several ways to fix this. One way is to change our Route component for Home to exact path instead of just path.

<Route exact path="/" component={Home} />

Try it now.

Recap

We imported the react-router-dom node module into our index.js with the BrowserRouter as Router and the Route components
We returned Router as the top level component in our React application
We defined three possible routes, each of which is doing the following:
- defining what URLs to match on
- defining what component should be rendered, should a match return true
- setting an attribute of exact, which explicitly states that you will only see the rendered component if you go to /about not /about/something_else or /abo.

We have made great progress so far!

Using `render`

If we look closely at our Routes, we see that our 'components' being passed to the component prop are merely functions defined above that return JSX. If we prefered, we could instead use the render prop and write inline code directly in our Route:

<Route path="/" render={() => <h1>Home!</h1>} />

While this inline style may be useful for very simple renders, it becomes unreasonable when we want to render larger, more complex, components, but this shows that we can be pretty flexible in how we set up our Routes.

If you are interested in seeing the 'under the hood' differences between the render and the component prop and when to use each take a moment to familiarize yourself with the Route documentation.

Now that we have the tools to enable routing, let's look into how we can enable users to trigger our Routes without requiring a manual change of the address bar.

NavLinks

What good are routes, if users don't know how to find them or what they are?

The React Router API provides two components that enable us to trigger our routing: Link and NavLink. They both have the same base level functionality that will update the browser URL and render the Route component. NavLink acts as a superset of Link, adding styling attributes to a rendered element when it matches the current URL.

Let's work on adding in the NavLink component to our application:

import React from 'react';
import ReactDOM from 'react-dom';
/* Add NavLink to importer */
import { BrowserRouter as Router, Route, NavLink } from 'react-router-dom';

/* Add basic styling for NavLinks */
const link = {
  width: '100px',
  padding: '12px',
  margin: '0 6px 6px',
  background: 'blue',
  textDecoration: 'none',
  color: 'white',
}

/* add the navbar component */
const Navbar = () =>
  <div>
    <NavLink
      to="/"
      /* set exact so it knows to only set activeStyle when route is deeply equal to link */
      exact
      /* add styling to Navlink */
      style={link}
      /* add prop for activeStyle */
      activeStyle={{
        background: 'darkblue'
      }}
    >Home</NavLink>
    <NavLink
      to="/about"
      exact
      style={link}
      activeStyle={{
        background: 'darkblue'
      }}
    >About</NavLink>
    <NavLink
      to="/login"
      exact
      style={link}
      activeStyle={{
        background: 'darkblue'
      }}
    >Login</NavLink>
  </div>;

const Home = () => <h1>Home!</h1>;

const About = () => <h1>This is my about component!</h1>;

const Login = () =>
  <form>
    <h1>Login</h1>
    <div>
      <input type="text" name="username" placeholder="Username" />
      <label htmlFor="username">Username</label>
    </div>
    <div>
      <input type="password" name="password" placeholder="Password" />
      <label htmlFor="password">Password</label>
    </div>
    <input type="submit" value="Login" />
  </form>;

ReactDOM.render((
  <Router>
    <divt>
      <Navbar />
      <Route exact path="/" component={Home} />
      <Route exact path="/about" component={About} />
      <Route exact path="/login" component={Login} />
    </divt>
  </Router>),
  document.getElementById('root')
);

Load up the browser again and you should see beautiful blue navlinks that load up the desired component. For more practice, implement /signup and /messages routes/navlinks that load in components.

Refactoring

In anticipation of a growing codebase, let's refactor by removing the components we defined in index.js and placing them in their own files in src/. Additionally, let's change them to classic class React.Components, i.e.:

// src/Home.js
import React from 'react';

class Home extends React.Component {
  render() {
    return <h1>Home!</h1>
  }
}

export default Home;

// src/About.js
import React from 'react';

class About extends React.Component {
  render() {
    return <h1>This is my about component!</h1>;
  }
}

export default About;

// src/Login.js
import React from 'react';

class Login extends React.Component {
  render() {
    return (
      <form>
        <h1>Login</h1>
        <div>
          <input type="text" name="username" placeholder="Username" />
          <label htmlFor="username">Username</label>
        </div>
        <div>
          <input type="password" name="password" placeholder="Password" />
          <label htmlFor="password">Password</label>
        </div>
        <input type="submit" value="Login" />
      </form>
    );
  }
}

export default Login;

// src/Navbar.js
import React from 'react'
import { NavLink } from 'react-router-dom';

const link = {
  width: '100px',
  padding: '12px',
  margin: '0 6px 6px',
  background: 'blue',
  textDecoration: 'none',
  color: 'white',
}

class Navbar extends React.Component {
  render() {
    return (
      <div>
        <NavLink
          to="/"
          /* set exact so it knows to only set activeStyle when route is deeply equal to link */
          exact
          /* add styling to Navlink */
          style={link}
          /* add prop for activeStyle */
          activeStyle={{
            background: 'darkblue'
          }}
        >Home</NavLink>
        <NavLink
          to="/about"
          exact
          style={link}
          activeStyle={{
            background: 'darkblue'
          }}
        >About</NavLink>
        <NavLink
          to="/login"
          exact
          style={link}
          activeStyle={{
            background: 'darkblue'
          }}
        >Login</NavLink>
      </div>
    )
  }
}

export default Navbar;

// src/index.js
import React from 'react';
import ReactDOM from 'react-dom';
import Home from './Home'
import About from './About'
import Login from './Login'
import Navbar from './Navbar'
import { BrowserRouter as Router, Route } from 'react-router-dom';

ReactDOM.render((
  <Router>
    <div>
      <Navbar />
      <Route exact path="/" component={Home} />
      <Route exact path="/about" component={About} />
      <Route exact path="/login" component={Login} />
    </div>
  </Router>),
  document.getElementById('root')
);

Resources

React Router Tutorial

View React Components As Routes on Learn.co and start learning to code for free.

Ahmed-Hassany/react-components-as-routes-recoded-sanaa-2019