LowFile-scopeJavaScript / TypeScript Plug & play

React's isMounted should not be used

Ensure that isMounted is not used in React components. This method is deprecated and can cause unreliable state updates. Suggest using cleanup functions or useRef instead.

Add to Mesrai Open workspace

Why this matters

The isMounted method is deprecated and hides warnings about improper state updates. Instead, use cleanup functions or other lifecycle methods to handle unmounted components safely.

Bad vs. good

Side-by-side examples engineers can pattern-match during review.

Avoid

class MyComponent extends React.Component {
  componentDidMount() {
    mydatastore.subscribe(this);
  }
  dataHandler() {
    if (this.isMounted()) { // Noncompliant: isMounted() hides the error
      //...
    }
  }
  render() {
    //... calls dataHandler()
  }
};

Prefer

class MyComponent extends React.Component {
  componentDidMount() {
    mydatastore.subscribe(this);
  }
  dataHandler() {
    //...
  }
  render() {
    //...
  }
  componentWillUnmount() {
    mydatastore.unsubscribe(this);
  }
}

More snippets

Bad

class MyComponent extends React.Component {
  componentDidMount() {
    mydatastore.subscribe(this);
  }
  dataHandler() {
    if (this.isMounted()) { // Noncompliant: isMounted() hides the error
      //...
    }
  }
  render() {
    //... calls dataHandler()
  }
};

Good

class MyComponent extends React.Component {
  componentDidMount() {
    mydatastore.subscribe(this);
  }
  dataHandler() {
    //...
  }
  render() {
    //...
  }
  componentWillUnmount() {
    mydatastore.unsubscribe(this);
  }
}

Related rules

From the same buckets as this rule.

Critical
Avoid Duplicating String Literals
Store repeated string literals in constants or variables to improve maintainability and reduce redundancy.
duplication-complexitymaintainability
Critical
Avoid Empty Methods
Detect methods that have an empty body. If a method is empty, ensure that a comment is present explaining why it remains unimplemented.
maintainabilityreadability-refactor
Critical
Avoid modifying built-in prototypes
Detect modifications to built-in prototypes. Modifying built-in objects can lead to compatibility issues and unexpected behavior. Recommend creating helper functions instead.
maintainabilitysecurity-hardening

Bad vs. good

Side-by-side examples engineers can pattern-match during review.

Avoid

class MyComponent extends React.Component {
  componentDidMount() {
    mydatastore.subscribe(this);
  }
  dataHandler() {
    if (this.isMounted()) { // Noncompliant: isMounted() hides the error
      //...
    }
  }
  render() {
    //... calls dataHandler()
  }
};

Prefer

class MyComponent extends React.Component {
  componentDidMount() {
    mydatastore.subscribe(this);
  }
  dataHandler() {
    //...
  }
  render() {
    //...
  }
  componentWillUnmount() {
    mydatastore.unsubscribe(this);
  }
}

More snippets

Bad

class MyComponent extends React.Component {
  componentDidMount() {
    mydatastore.subscribe(this);
  }
  dataHandler() {
    if (this.isMounted()) { // Noncompliant: isMounted() hides the error
      //...
    }
  }
  render() {
    //... calls dataHandler()
  }
};

Good

class MyComponent extends React.Component {
  componentDidMount() {
    mydatastore.subscribe(this);
  }
  dataHandler() {
    //...
  }
  render() {
    //...
  }
  componentWillUnmount() {
    mydatastore.unsubscribe(this);
  }
}

Related rules

From the same buckets as this rule.

Critical

Avoid Duplicating String Literals

Store repeated string literals in constants or variables to improve maintainability and reduce redundancy.

duplication-complexitymaintainability

Critical

Avoid Empty Methods

Detect methods that have an empty body. If a method is empty, ensure that a comment is present explaining why it remains unimplemented.

maintainabilityreadability-refactor

Critical

Avoid modifying built-in prototypes

Detect modifications to built-in prototypes. Modifying built-in objects can lead to compatibility issues and unexpected behavior. Recommend creating helper functions instead.

maintainabilitysecurity-hardening