gem-hunter

• Create nested routes in React Router
• Use URL parameters in React Router
• Use the useRouteMatch and useParams hooks to access information about React Router's internal state

Have you ever used Apple's Messages app for your Mac? What about YouTube? These apps use a type of list/detail interface which consists of a list of all instances of a resource (messages, videos, emails, etc.) from which we can select specific items. Clicking on one will trigger a more detailed display of that specific item on another portion of the screen instead of displaying an entirely new page. (You may also see this pattern referred to as the master/detail pattern.) With this design, a user can navigate through many items in a list, looking at item details without ever leaving the page they are on.

Consider how we might create this sort of design in regular React, without using Routes: we could create two sibling components, one for the list, and the other for the details of a specific item. We could call them List and Item. Then, we create one parent component for both that handles state. The parent component could keep track of all the list data and which particular item is currently selected, and pass down props to both components.

This would work, but there are limitations. One problem with this approach is that changing state won't change the URL, meaning there is no way to provide a link directly to one particular item from our list of resources.

Apps like YouTube display a list of videos, and clicking on any one video will load it, but every time you open a particular video, the URL changes. YouTube assigns unique values to each video (something like dQw4w9WgXcQ). When viewing that video, the value is listed as part of the URL. This value is a URL parameter and allows for convenient sharing and bookmarking.

https://www.youtube.com/watch?v=dQw4w9WgXcQ

https    :// www.youtube.com / watch ? v             = dQw4w9WgXcQ

protocol :// domain          / path  ? parameter_key = parameter_value

In this lesson, we will learn how to use React Router to set up the list/detail pattern. Specifically, we will learn how to:

• set up nested Routes for list and item components such that clicking on an item will display its details along with the list
• set up our Routes to produce shareable URLs, i.e., URLs that contain a parameter corresponding to the specific resource we want to display

Our final component hierarchy will look like this:

└── App
    ├── NavBar
    └── MoviesPage
        |   MoviesList
        └── MovieShow

The App component will render the NavBar and MoviesPage components and is where we'll define our top-level Routes. The MoviesPage component will be the parent to the two presentational components, MoviesList and MovieShow, and is where we'll set up our nested route.

So far, we've only seen Routes side by side, but that won't really work in this example. When a list item is clicked, we want to see the details of that item, but we still want the list to display.

Instead of listing two Routes side by side, we can set up the list/detail pattern by using React Router to make our Item component the child of the List component.

Think of YouTube again for a moment. Let's pretend that visiting /videos displays a List of videos. Clicking on any video should keep our list of videos on the page, but also display details for the selected video. In addition, the URL should be updated to /videos/:videoId, where :videoId is a unique value that identifies the selected video. (Note that this isn't exactly how YouTube works but the concepts are similar.) Using nested React Router, we can write our application so one component — the List of videos — renders using a Route that matches the path /videos. Then, within the List, we can nest a second Route that renders the appropriate Item when the path matches /videos/:videoId.

Let's build this out!

To begin, let's take a look at our starter code. First, we have our App component. App has some dummy movie data provided in state for us (normally, we would likely be fetching this info).

const [movies, setMovies] = useState([
  { id: 1, title: "A River Runs Through It" },
  { id: 2, title: "Se7en" },
  { id: 3, title: "Inception" }
]);

Looking at the index.js file, we see that we have Router wrapping our App. All JSX wrapped within Router can use Routes, including the JSX from any child components. In our case, that is all of our components.

App has two Route elements:

<Switch>
  <Route path="/movies">
    <MoviesPage movies={movies} />
  </Route>
  <Route exact path="/">
    <div>Home</div>
  </Route>
</Switch>

Looking at the MoviesPage component, this component is responsible for loading our MoviesList component and passing in the movies we received from App.

// ./src/components/MoviesPage.js
import React from "react";
import { Route } from "react-router-dom";
import MoviesList from "./MoviesList";

function MoviesPage({ movies }) {
  return (
    <div>
      <MoviesList movies={movies} />
    </div>
  );
}

export default MoviesPage;

At the moment, our MoviesPage component doesn't do much. It is simply the middle component between App and MoviesList, but we will come back to this component in a moment. Right now, if we try to run our React app, we get an error because MoviesList is not defined yet!

Let's create our MoviesList component to render a <Link> for each movie:

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

function MoviesList({ movies }) {
  const renderMovies = movies.map((movie) => (
    <li key={movie.id}>
      <Link to={`/movies/${movie.id}`}>{movie.title}</Link>
    </li>
  ));

  return <ul>{renderMovies}</ul>;
}

export default MoviesList;

The movies prop has been passed from App to MoviesPage, then again to MoviesList.

The movies prop is an array containing each movie object. We're mapping over this array to create an li element and a Link for each movie. We are using the id of each movie as the key attribute and in the relative href for our Links, and are using the title of each movie as the text for our Links.

In the Link, we've used interpolation to insert movie.id into our path to make it dynamic:

to={`/movies/${movie.id}`}

Now, if we start up the app, we'll see that if a user goes to the /movies route, MoviesList will render a list of clickable router links. Clicking on one of the movie names will update the URL to display that movie's id. Next, we'll add in our nested route within MoviesPage so that going to /movies/:movieId will display details about a given movie using a MovieShow component.

To start, let's create our MovieShow component. Later on, we will see that this component will need to dynamically figure out which movie it should render.

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

function MovieShow() {
  return (
    <div>
      <h3>Movies Show Component!</h3>
    </div>
  );
}

export default MovieShow;

Next, we'll import MovieShow into MoviesPage and add a nested route in our src/components/MoviesPage.js file to display the MovieShow container if the route matches /movies/:movieId. We also need to import the useRouteMatch hook from React Router, which we'll use to identify the matched route.

// .src/components/MoviesPage.js
import React from "react";
// import the custom `useRouteMatch` hook from React Router
import { Route, useRouteMatch } from "react-router-dom";
import MoviesList from "./MoviesList";
// import the MovieShow component
import MovieShow from "./MovieShow";

function MoviesPage({ movies }) {
  // useRouteMatch returns a special object with information about
  // the currently matched route
  const match = useRouteMatch();
  console.log(match);

  return (
    <div>
      <MoviesList movies={movies} />
      {/* 
        we can use the current URL from the `match` object as part of the path;
        this will generate a url like "/movies/:movieId"
      */}
      <Route path={`${match.url}/:movieId`}>
        <MovieShow />
      </Route>
    </div>
  );
}

export default MoviesPage;

In the code above, calling useRouteMatch() inside our component gives us an object that contains the current URL. We have assigned that object to the variable match, which we then use to specify what content to render. Specifically, match.url gives us the /videos part of the url, and we append the :movieId for the particular video we want to display. :movieId represents a parameter. If we visit http://localhost:3000/movies/1, the value of movieId will be "1".

Going back to our MoviesList component, remember that when movies is mapped, our Links are each getting a unique path in the to={...} attribute, since each movieId is different.

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

function MoviesList({ movies }) {
  const renderMovies = movies.map((movie) => (
    <li key={movie.id}>
      <Link to={`/movies/${movie.id}`}>{movie.title}</Link>
    </li>
  ));

  return <ul>{renderMovies}</ul>;
}

export default MoviesList;

We have now set up the receiving end of the movie links so React knows what component to render when an individual movie's link is clicked.

Refresh the page at /movies. Now, clicking a link changes the route, but we're not actually seeing any content about that movie on our MovieShow page. You should only see the text Movies Show Component! under the navigation and movie links.

Just as we saw with App, the data we want to display on a particular MovieShow page is available in its parent, MoviesPage, as props. For MovieShow to display this content, we will need to make our movies collection available within MovieShow.

// .src/components/MoviesPage.js
import React from "react";
import { Route, useRouteMatch } from "react-router-dom";
import MoviesList from "./MoviesList";
import MovieShow from "./MovieShow";

function MoviesPage({ movies }) {
  const match = useRouteMatch();

  return (
    <div>
      <MoviesList movies={movies} />
      <Route path={`${match.url}/:movieId`}>
        {/* adding the movies object as a prop to MovieShow */}
        <MovieShow movies={movies} />
      </Route>
    </div>
  );
}

export default MoviesPage;

This isn't enough though — MovieShow now has all the movies, but it doesn't know which movie it should display. This information is only available from the URL. Remember — when we click a Link to a movie, it adds that movie's id to the URL as a parameter. We need to get that parameter out of the URL and into MovieShow.

Just like we can use the useRouteMatch hook to get information about the URL for the current route, we can also use another hook to get the dynamic params from the URL: the useParams hook!

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

function MovieShow({ movies }) {
  // call useParams to access the `params` from the url
  const params = useParams();
  console.log(params);

  const movie = movies.find(movie => movie.id === parseInt(params.movieId))

  return (
    <div>
      {/* And here we access the `movieId` stored in `params` to render 
        information about the selected movie */}
      <h3>{movie.title}</h3>
    </div>
  );
}

export default MovieShow;

Here, we've got our movies as an array in props. We also have our params object which was returned from useParams based on the current URL. In this case, we only have the one parameter, movieId, which we defined in the <Route> in MoviesPage. We retrieve the movieId for the desired movie from the params object, then use that to find the movie from the movies array resulting in the correct movie title being displayed!

Note that the datatype in our params object is a string, while the datatype of our movie.id is a integer. We can use JavaScript's built in parseInt function to handle the type conversion!

We've succeeded in creating a list/detail interface in which the list of movies is always present when viewing a particular movie's details. Clicking through the links changes the URL. With this setup, users of this site could bookmark or share the URL for a specific movie!

With our main task completed, let's take a quick step back and ask a question — what happens in this app when we visit http://localhost:3000/movies without a particular movieId parameter? Well, MoviesPage renders due to the top-level /movies Route, but MoviesPage will only render MoviesList. There is no default Route, so we don't see anything except the list. If we want to create a default Route here — i.e., if we want to specify what users will see if they navigate to /movies — we can do so using the match variable from useRouteMatch() once again:

// .src/components/MoviesPage.js
import React from "react";
import { Route, useRouteMatch } from "react-router-dom";
import MoviesList from "./MoviesList";
import MovieShow from "./MovieShow";

function MoviesPage({ movies }) {
  const match = useRouteMatch();

  return (
    <div>
      <MoviesList movies={movies} />

      {/* Adding code to show a message to the user to select a movie if they haven't yet */}
      <Route exact path={match.url}>
        <h3>Choose a movie from the list above</h3>
      </Route>

      <Route path={`${match.url}/:movieId`}>
        <MovieShow movies={movies} />
      </Route>
    </div>
  );
}

export default MoviesPage;

Now, when we visit http://localhost:3000/movies, we see a message that only appears if there is no additional movieId at the end of the URL. This is the nested version of a default route. We can't just write exact path="/" since these Routes will only render inside the /movies Route.

As we have learned in this section, React Router enables us to set up routes that allow our users to navigate to different "pages" in our applications. The routes we define can be static (e.g., /movies) or we can include a parameter (e.g., /movies/:movieId) to make it dynamic. React Router will also update the URL in the browser to reflect whichever page the user has navigated to.

We are also able to nest <Route> components within each other, which allows us to build single-page applications in React that behave like they have many pages. Using the useRouteMatch hook, we can nest a second Route that extends the URL path of the first. We can actually nest Routes as many times as we would like, so if we wanted, we could go fully RESTful and create nested Routes inside MovieShow as well, allowing us to write URL paths that would look something like this:

http://localhost:3000/movies
http://localhost:3000/movies/new
http://localhost:3000/movies/:movieId
http://localhost:3000/movies/:movieId/edit

In this lesson, we learned how to set up nested routes to create a list/detail interface. Specifically, we learned how we can display a list of items along with details about an individual item on the same page. To get this to work, we needed to complete the following steps:

• In the top-level component (App.js in this case), create our "parent" routes and render <MoviesPage>
• In MoviesPage.js, render <MoviesList>
• In MoviesList.js, iterate through the movies array and create a dynamic Link for each movie using its id
• Back in MoviesPage.js, import useRouteMatch and create the child route by combining the current url with the :movieId parameter; inside the child route, render <MovieShow>, passing the movies array as props
• In MovieShow.js, import useParams; use the :movieId from the params object to find the correct movie from the movies array and display it on the page

In setting up our nested routes, we made use of two hooks provided by React Router: useRouteMatch and useParams. The first is used to retrieve the URL of the current page, and the second allows us to access the value of any parameters we're using in our routes. The two together, along with the movies object, gave us all the tools we needed to create dynamic routes for individual movies and to display a movie's information when its link is clicked.

In the early days of the internet, we would have had to create separate HTML pages for each movie in this application. Now, with React, we can write abstract components that fill in the data for each 'page' on demand. Very cool!

• useRouteMatch
• useParams