Tutorial

React Router: Optional Parameters

Published on June 20, 2017
author

Matthew Garcia

React Router: Optional Parameters

While we believe that this content benefits our community, we have not yet thoroughly reviewed it. If you have any suggestions for improvements, please let us know by clicking the “report an issue“ button at the bottom of the tutorial.

React Router makes it easy to use parameters, but these are mandatory by default. While this is enough for most cases, there are some situations where optional parameters would be beneficial.

Creating a Route With an Optional Parameter

As with regular parameters, declaring an optional parameter is just a matter of the path property of a Route; any parameter that ends with a question mark will be treated as optional:

class App extends Component {
  render() {
    return (
      <BrowserRouter>
        <div>
          {/* Optional parameters are defined by placing a question mark at the end of a parameter. */}
          {/* In this case, `line` is an optional parameter. */}
          {/* Optional parameters will be passed to the component, but will be undefined if not present in the URL. */}
          <Route path="/Lyrics/:song/:line?" component={LyricSheet}/>
        </div>
      </BrowserRouter>
    );
  }
}

The route will be rendered if it matches the path, with or without the optional parameter. So ‘/Lyrics/Spoonman’ and ‘/Lyrics/Spoonman/3’ would both be accepted.

Using Optional Parameters

Optional parameters are passed alongside mandatory ones as props. But if they’re not in the URL, they’ll be undefined:

export default function LyricSheet({ match }) {
  const {line, song} = match.params;
  // Since `line` is an optional parameter, it'll either be undefined or a string.
  const lineNumber = line ? parseInt(line, 10) : -1;
  // Get the lyrics to the song.
  const lyrics = getLyrics(song)
    // Map the lyrics to components.  If `index` is `lineNumber`, set `highlight` to `true`.
    .map((lyric, index) => (<LyricLine highlight={index === lineNumber} key={index} lyric={lyric} />));
  return (
    <div>{lyrics}</div>
  );
}

The component will be rendered to show the lyrics of song. If the optional parameter line is defined, that line will be highlighted. You’ve probably seen something like this if you’ve flipped through a file on GitHub.

If you’d like to learn more about React, take a look at our How To Code in React.js series, or check out our React topic page for exercises and programming projects.

Thanks for learning with the DigitalOcean Community. Check out our offerings for compute, storage, networking, and managed databases.

Learn more about our products


About the authors
Default avatar
Matthew Garcia

author

Still looking for an answer?

Ask a questionSearch for more help

Was this helpful?
 
Leave a comment


This textbox defaults to using Markdown to format your answer.

You can type !ref in this text area to quickly search our full set of tutorials, documentation & marketplace offerings and insert the link!

Try DigitalOcean for free

Click below to sign up and get $200 of credit to try our products over 60 days!

Sign up

Join the Tech Talk
Success! Thank you! Please check your email for further details.

Please complete your information!

Featured on Community

Get our biweekly newsletter

Sign up for Infrastructure as a Newsletter.

Hollie's Hub for Good

Working on improving health and education, reducing inequality, and spurring economic growth? We'd like to help.

Become a contributor

Get paid to write technical tutorials and select a tech-focused charity to receive a matching donation.

Welcome to the developer cloud

DigitalOcean makes it simple to launch in the cloud and scale up as you grow — whether you're running one virtual machine or ten thousand.

Learn more
DigitalOcean Cloud Control Panel