no-did-mount-set-state

Keywords: React, componentDidMount, setState, lifecycle, performance, ESLint rule, LLM-optimized

Prevent calling setState in componentDidMount. This rule is part of eslint-plugin-react-features.

Quick Summary

Rule Details

Calling setState immediately in componentDidMount causes an additional render cycle. Initial state should be set in the constructor or derived from props.

Why This Matters

Examples

❌ Incorrect

class UserProfile extends React.Component {
  state = { user: null };
  
  componentDidMount() {
    // BAD: Immediate setState causes extra render
    this.setState({ loading: true });
    
    // This is also problematic
    this.setState({
      windowWidth: window.innerWidth
    });
  }
}

✅ Correct

mounted

Configuration Examples

Basic Usage

{
  rules: {
    'react-features/no-did-mount-set-state': 'warn'
  }
}

Related Rules

• no-did-update-set-state - Similar for componentDidUpdate
• react-class-to-hooks - Migrate to hooks

Further Reading

• componentDidMount - React docs
• State Initialization - Constructor patterns

Known False Negatives

The following patterns are not detected due to static analysis limitations:

Dynamic Variable References

Why: Static analysis cannot trace values stored in variables or passed through function parameters.

// ❌ NOT DETECTED - Prop from variable
const propValue = computedValue;
<Component prop={propValue} /> // Computation not analyzed

Mitigation: Implement runtime validation and review code manually. Consider using TypeScript branded types for validated inputs.

Wrapped or Aliased Functions

Why: Custom wrapper functions or aliased methods are not recognized by the rule.

// ❌ NOT DETECTED - Custom wrapper
function myWrapper(data) {
  return internalApi(data); // Wrapper not analyzed
}
myWrapper(unsafeInput);

Mitigation: Apply this rule's principles to wrapper function implementations. Avoid aliasing security-sensitive functions.

Imported Values

Why: When values come from imports, the rule cannot analyze their origin or construction.

// ❌ NOT DETECTED - Value from import
import { getValue } from './helpers';
processValue(getValue()); // Cross-file not tracked

Mitigation: Ensure imported values follow the same constraints. Use TypeScript for type safety.