gem-hunter

• Add react-router-dom to an existing React application
• Create multiple client-side routes

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 based on state 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 at www.loveforsoils.com/favorites. Enter React Router: a routing library for React that allows us to link to specific URLs and conditionally render components depending on which URL is displayed.

React Router is a collection of navigational components and custom hooks that are implemented using declarative programming and compose with the components in your application. Whether you want to have bookmark-able 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!

To demonstrate some of the key features of React Router, we have an exercise to code along with, so let's get going!

To get started, clone down this repo and run npm install.

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

// ./src/index.js
import React from "react";
import ReactDOM from "react-dom";

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

function App() {
  return <Home />;
}

ReactDOM.render(<App />, document.getElementById("root"));

To start using React Router, we need to install react-router-dom:

$ npm install react-router-dom@5

Note: make sure to include @5 at the end of the install command to install React Router version 5 instead of version 6.

To start implementing routes, we first need to import BrowserRouter and Route from react-router-dom:

// .src/index.js

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

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

// Step 2. Use <Route> components to define client-side routes in our app
function App() {
  return (
    <Route path="/">
      <Home />
    </Route>
  );
}

// Step 3. Use <BrowserRouter> component to wrap the entire application and provide React Router context features
ReactDOM.render(
  <BrowserRouter>
    <App />
  </BrowserRouter>,
  document.getElementById("root")
);

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

1. The BrowserRouter component is the base for our application's routing. It is where we declare how React Router will be used. Notice that the BrowserRouter component is wrapped around our entire application. This lets us use the Route component and other React Router components anywhere in our app.
2. The Route component is in charge of saying: "when the URL matches this specified path, render this child component." This handles the conditional rendering based on the URL that we described earlier. The Route component has one prop in our example: path.

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 Home!.

In the last two steps, we learned how to set up the basic BrowserRouter 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, Route } from "react-router-dom";

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

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

function Login() {
  return (
    <div>
      <h1>Login</h1>
      <form>
        <div>
          <input type="text" name="username" placeholder="Username" />
        </div>
        <div>
          <input type="password" name="password" placeholder="Password" />
        </div>
        <input type="submit" value="Submit" />
      </form>
    </div>
  );
}

Now let's add our /about and /login routes to our routing logic:

// ./src/index.js
function App() {
  return (
    <div>
      <Route path="/">
        <Home />
      </Route>
      <Route path="/about">
        <About />
      </Route>
      <Route path="/login">
        <Login />
      </Route>
    </div>
  );
}

If you go back to the browser you will see that it looks the same — our Home component is displaying as before. Now try manually typing in the URL locations for /, /about, and /login. Do you see the other components rendering?

You may have noticed the strange 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.

If we had a header component we wanted to be displayed no matter which route was hit, this behavior would be desirable. Otherwise, there are several ways to fix this. One way to give more predictable behavior to our Routes is to use the Switch component:

// ./src/index.js
import { BrowserRouter, Route, Switch } from "react-router-dom";

// ...

function App() {
  return (
    <Switch>
      <Route path="/">
        <Home />
      </Route>
      <Route path="/about">
        <About />
      </Route>
      <Route path="/login">
        <Login />
      </Route>
    </Switch>
  );
}

Now, instead of rendering all routes that match the current URL, it will only render the first route that matches any part of the URL. Currently, we'll always be rendering the Home component. We can fix this by moving the route for / to the bottom of our Switch component:

function App() {
  return (
    <Switch>
      <Route path="/about">
        <About />
      </Route>
      <Route path="/login">
        <Login />
      </Route>
      <Route path="/">
        <Home />
      </Route>
    </Switch>
  );
}

Try it out again! Go to /about and you'll only see the About component being displayed.

There's one other prop we can use on our routes to give more control over whether that route will match the given url: exact. First, to demonstrate the issue, try visiting a URL that isn't covered by any of our routes, like /wat. We'll still see our Home component being displayed, because / is a partial match for /wat.

To fix this, try adding exact to the Route component rendering our Home component:

<Route exact path="/">
  <Home />
</Route>

Now, Home will only display when the URL is exactly /.

The exact prop looks a bit different from our other props — where's the =? This syntax is short for exact={true}! You'll see the same syntax used in HTML for boolean attributes: if the attribute is present, it's true, if it's absent, it's false.

• We imported the BrowserRouter and the Route components from the react-router-dom package into our index.js file
• We wrapped BrowserRouter around 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
  • for our / route, setting a prop of exact, which ensures that you will only see the component if you go to the exact path.

We have made great progress so far!

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.

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

React Router provides two components that enable us to trigger our routing: Link and NavLink. They both have the same base level functionality:

• They render an <a> tag to the DOM
• When the <a> tag is clicked, they change the URL and tell React Router to re-render our routes, displaying the component that matches the new URL

NavLink acts as a superset of Link, adding styling attributes to a rendered element when it matches the current URL. NavLink works well for creating a navigation bar, since it allows us to add styling to indicate which link is currently selected. Link is a good option for creating standard hyperlinks. For this example, we will be using NavLink; we will see examples of using Link in later lessons.

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

import React from "react";
import ReactDOM from "react-dom";
/* Add NavLink to import */
import { BrowserRouter, Route, NavLink, Switch } from "react-router-dom";

/* Add basic styling for NavLinks */
const linkStyles = {
  display: "inline-block",
  width: "50px",
  padding: "12px",
  margin: "0 6px 6px",
  background: "blue",
  textDecoration: "none",
  color: "white",
};

/* define the NavBar component */
function NavBar() {
  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={linkStyles}
        /* add prop for activeStyle */
        activeStyle={{
          background: "darkblue",
        }}
      >
        Home
      </NavLink>
      <NavLink
        to="/about"
        exact
        style={linkStyles}
        activeStyle={{
          background: "darkblue",
        }}
      >
        About
      </NavLink>
      <NavLink
        to="/login"
        exact
        style={linkStyles}
        activeStyle={{
          background: "darkblue",
        }}
      >
        Login
      </NavLink>
    </div>
  );
}

function Home() {
  return <h1>Home!</h1>;
}

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

function Login() {
  return (
    <div>
      <h1>Login</h1>
      <form>
        <div>
          <input type="text" name="username" placeholder="Username" />
        </div>
        <div>
          <input type="password" name="password" placeholder="Password" />
        </div>
        <input type="submit" value="Submit" />
      </form>
    </div>
  );
}

/* add the NavBar component to our App component */
function App() {
  return (
    <div>
      <NavBar />
      <Switch>
        <Route path="/about">
          <About />
        </Route>
        <Route path="/login">
          <Login />
        </Route>
        <Route path="/">
          <Home />
        </Route>
      </Switch>
    </div>
  );
}

ReactDOM.render(
  <BrowserRouter>
    <NavBar />
    <Switch>
      <Route exact path="/about">
        <About />
      </Route>
      <Route exact path="/login">
        <Login />
      </Route>
      <Route exact path="/">
        <Home />
      </Route>
    </Switch>
  </BrowserRouter>,
  document.getElementById("root")
);

Load up the browser again and you should see beautiful blue NavLinks that load up the desired component. Note that, because we've rendered the NavBar component outside the Switch component, it appears on each page, as desired.

For more practice, implement /signup and /messages routes, NavLinks and 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/components. You can also see the completed version of this code in the solution branch.

// src/components/Home.js
import React from "react";

function Home() {
  return <h1>Home!</h1>;
}

export default Home;

// src/components/About.js
import React from "react";

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

export default About;

// src/components/Login.js
import React from "react";

function Login() {
  return (
    <div>
      <h1>Login</h1>
      <form>
        <div>
          <input type="text" name="username" placeholder="Username" />
        </div>
        <div>
          <input type="password" name="password" placeholder="Password" />
        </div>
        <input type="submit" value="Submit" />
      </form>
    </div>
  );
}

export default Login;

// src/components/NavBar.js
import React from "react";
import { NavLink } from "react-router-dom";

const linkStyles = {
  display: "inline-block",
  width: "50px",
  padding: "12px",
  margin: "0 6px 6px",
  background: "blue",
  textDecoration: "none",
  color: "white",
};

function NavBar() {
  return (
    <div>
      <NavLink
        to="/"
        exact
        style={linkStyles}
        activeStyle={{
          background: "darkblue",
        }}
      >
        Home
      </NavLink>
      <NavLink
        to="/about"
        exact
        style={linkStyles}
        activeStyle={{
          background: "darkblue",
        }}
      >
        About
      </NavLink>
      <NavLink
        to="/login"
        exact
        style={linkStyles}
        activeStyle={{
          background: "darkblue",
        }}
      >
        Login
      </NavLink>
    </div>
  );
}

export default NavBar;

// src/components/App.js
import React from "react";
import { Route, Switch } from "react-router-dom";
import Home from "./Home";
import About from "./About";
import Login from "./Login";
import NavBar from "./NavBar";

function App() {
  return (
    <div>
      <NavBar />
      <Switch>
        <Route exact path="/about">
          <About />
        </Route>
        <Route exact path="/login">
          <Login />
        </Route>
        <Route exact path="/">
          <Home />
        </Route>
      </Switch>
    </div>
  );
}

export default App;

// src/index.js
import React from "react";
import ReactDOM from "react-dom";
import { BrowserRouter } from "react-router-dom";
import App from "./components/App";

ReactDOM.render(
  <BrowserRouter>
    <App />
  </BrowserRouter>,
  document.getElementById("root")
);

You've now seen all the core functionality of React Router required for client-side routing! We've met the requirements so that our app can:

• Conditionally render a different component based on the URL (using the <Route> and <Switch> components)
• Change the URL using JavaScript, without making a GET request and reloading the HTML document (using the <Link> or <NavLink> components)

In the coming lessons, we'll explore more of the advanced functionality provided by React Router. You are also strongly encouraged to look at the React Router docs, and in particular at the examples section, to get more ideas on how to use React Router to build common features in your own applications.

• React Router docs