react/no-is-mounted

isMounted() only exists on components made with createReactClass. In a class that extends React.Component, this.isMounted is undefined and the call throws.

It's mostly used to skip a setState after the component is gone. That hides the real problem: a request, timer or subscription that's still running and still holds on to the component. Cancel it in componentWillUnmount.

Configure

Off by default. To turn it on:

[lint.rules]
"react/no-is-mounted" = "error" # or "warn"

Examples

Reported:

class Profile extends React.Component {
  componentDidMount() {
    loadUser(this.props.id).then(user => {
      if (this.isMounted()) {
        this.setState({ user });
      }
    });
  }
}

Not reported:

class Profile extends React.Component {
  controller = new AbortController();

  componentDidMount() {
    loadUser(this.props.id, { signal: this.controller.signal }).then(user => {
      this.setState({ user });
    });
  }

  componentWillUnmount() {
    this.controller.abort();
  }
}