<!--
title: Extract complex logical expressions
domain: runtimes
topic: Code Style
language: TypeScript
source: microsoft/typescript
updated: 2025-06-09
url: https://awesomereviewers.com/reviewers/typescript-extract-complex-logical-expressions/
-->

Complex logical expressions should be extracted into well-named variables or functions to improve code readability and maintainability. This applies to:
- Boolean conditions with multiple parts
- Repeated logic across multiple locations
- Complex property access chains

Example - Before:
```typescript
const classOrInterfaceDeclaration = declaration.parent?.kind === SyntaxKind.Constructor && getSyntacticModifierFlags(declaration) & ModifierFlags.AccessibilityModifier ? declaration.parent.parent : declaration.parent;
```

Example - After:
```typescript
const isConstructorParamWithAccessModifier = declaration.parent?.kind === SyntaxKind.Constructor && 
    getSyntacticModifierFlags(declaration) & ModifierFlags.AccessibilityModifier;
const classOrInterfaceDeclaration = isConstructorParamWithAccessModifier ? declaration.parent.parent : declaration.parent;
```

The extracted variable name should clearly describe the condition's purpose. For frequently used conditions, consider extracting them into helper functions that can be reused across the codebase.