Sentry Answers>React>

Modifying State of a Component Directly

Modifying State of a Component Directly

Evan Hicks

—

The ProblemJump To Solution

The state of a component is managed internally by React. Updating the state of a component directly can have unintended consequences that can be difficult to debug.

Click to Copy
class Counter extends Component {
    constructor(props) {
        super(props)
        this.state = {
            counter: 0,
        }
    }

    increment() {
        this.state.counter = this.state.counter + this.props.increment
    }
}

If the state is updated directly as in the example above, the component will not rerender since the state is compared shallowly. Additionally, the update may be lost if there are other state changes queued asynchronously using setState.

Another common problem is using the current state/props to update the new state.

Click to Copy
class Counter extends Component {
    constructor(props) {
        super(props)
        this.state = {
            counter: 0,
        }
    }

    increment() {
        this.setState({
            counter: this.state.counter + this.props.increment
        })
    }
}

This will potentially cause issues due to a potential race condition between other state/prop changes and this particular state update. What happens if the props and/or state change before this state update happens?

The Solution

The solution for the first example is to always use the setState function to ensure state changes are properly queued. For the second problem, React provides a different version of setState that takes a function instead of an object.

Click to Copy
class Counter extends Component {
    constructor(props) {
        super(props)
        this.state = {
            counter: 0,
        }
    }

    increment() {
        this.setState((prevState, props) => ({
            counter: prevState.counter + props.increment
        })
    }
}

This will ensure that the state change happens with the correct version of the previous state and props.

Further Reading

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

  • Syntax.fmReact Server Components
  • Sentry BlogFixing memoization-breaking re-renders in React
  • Syntax.fm logo
    Listen to the Syntax Podcast

    Tasty Treats for Web Developers brought to you by Sentry. Web development tips and tricks hosted by Wes Bos and Scott Tolinski

    Listen to Syntax

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
© 2024 • Sentry is a registered Trademark
of Functional Software, Inc.