/react-components-as-routes-london-web-career-021819

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Introduction to React Router

Objectives

  1. Describe React Router's approach to client-side routing
  2. Explain how React Router allows building a route tree as a component
  3. 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 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

Step 1: 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 the src/index.js file 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. Let's install that package now.

npm install react-router-dom

We now want to import the BrowserRouter component as a Router and the Route component and inject it into our Home component.

// .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="/" render={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 render. The Route component is in charge of saying: "when the url matches this specified path, render this specified component".

Let's try it. Run npm start to boot up the application and then point your url to 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="/" render={Home} />
      <Route exact path="/about" render={About} />
      <Route exact path="/login" render={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 or a fragment:

ReactDOM.render((
  <Router>
    <React.Fragment>
      <Route path="/" render={Home} />
      <Route exact path="/about" render={About} />
      <Route exact path="/login" render={Login} />
    </React.Fragment>
  </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. 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. Because we are programmers who think ahead, and want to write code that can scale, let's refactor!

Components as Props

If we look closely, we see our 'components' being passed to the render props are merely functions defined above that return JSX.

So far, we have been using the Route component's render prop to describe what should be rendered when a match occurs. As an alternative to defining the arrow functions for Home, About, and Login, we could have simply done it inline, i.e.:

<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. 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.:

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

Now, let's refactor our Router component in index.js to use your class components:

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

Take note: we changed the render prop to component within our Route components. As it turns out, the Route component API has a prop called component.

What's the difference between using the render prop and the component prop in our Route component? In terms of user experience in our application, there is none!

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. For ease of display, we will work as if we still have all of our components in one file. If you have broken them out into individual component files, update accordingly:

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>
    <React.Fragment>
      <Navbar />
      <Route exact path="/" component={Home} />
      <Route exact path="/about" component={About} />
      <Route exact path="/login" component={Login} />
    </React.Fragment>
  </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.

Resources

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