Answers by Sentry

Warning: componentWillMount has been Renamed, and is not Recommended for Use

Nisanthan Nanthakumar

The Problem

Warning: componentWillMount has been renamed, and is not recommended for use

Initializing state

// Before
class AppComponent extends React.Component {
  state = {};

  componentWillMount() {
    this.setState({
      selected: this.props.selected,
      color: 'red',
    });
  }
}

Fetching external data

// Before
class AppComponent extends React.Component {
  state = {
    data: null,
  };

  componentWillMount() {
    fetch('https://sentry.io/data').then(res => {
      this.setState({ data: res.json() });
    });
  }
}

The Solution

Starting in React version 16.3, the following component lifecycle methods are being phased out.

  • componentWillMount
  • componentWillReceiveProps
  • componentWillUpdate

If you want to use these methods, prefix the methods with UNSAFE_ . These methods are considered “unsafe” because the React team expect code that depends on these methods to be more likely to have bugs in future versions of React.

Depending on the objective of the code, you can remove the use of componentWillMount entirely with other lifecycle methods.

The solution is to move the state initialization to the constructor or to a property initializer, like so:

// After
class AppComponent extends React.Component {
  state = {
    selected: this.props.selected,
    color: 'red',
  };
}

The solution is to move data-fetching into componentDidMount:

// After
class AppComponent extends React.Component {
  state = {
    data: null,
  };

  componentDidMount() {
    fetch('https://sentry.io/data').then(res => {
      this.setState({ data: res.json() });
    });
  }
}

Further Reading

If you’re looking to get a deeper understanding of how JavaScript application monitoring works, take a look at the following articles:

Get Started With Sentry

Get actionable, code-level insights to resolve JavaScript performance bottlenecks and errors.

  1. Create a free Sentry account

  2. Create a JavaScript project and note your DSN

  3. Grab the Sentry JavaScript SDK

<script src="https://browser.sentry-cdn.com/7.110.1/bundle.min.js"></script>
  1. Configure your DSN
Sentry.init({ dsn: 'https://<key>@sentry.io/<project>' });

Loved by over 4 million developers and more than 90,000 organizations worldwide, Sentry provides code-level observability to many of the world’s best-known companies like Disney, Peloton, Cloudflare, Eventbrite, Slack, Supercell, and Rockstar Games. Each month we process billions of exceptions from the most popular products on the internet.

learn more about sentryjoin our discord
Share on Twitter
Bookmark this page
Ask a questionJoin the discussion

Related Answers

A better experience for your users. An easier life for your developers.

Try Sentry For FreeRequest a Demo
    TwitterGitHubDribbbleLinkedinDiscord
© 2024 • Sentry is a registered Trademark
of Functional Software, Inc.