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338What Interfaces Are
339Basic Interface Syntax
340Interface vs Object Type Literal
341Optional Properties in Interfaces
342Readonly Properties in Interfaces
343Method Signatures in Interfaces
344Index Signatures in Interfaces
345Implementing Interfaces with Classes
346Multiple Interface Implementation
347Interfaces for Function Types
348What Is a Type Alias?
349Basic Type Alias Syntax
350Aliasing Primitive and Literal Types
351Aliasing Object Types
352Aliasing Function Types
353Aliasing Union Types
354Aliasing Intersection Types
355Type Aliases Are Not Nominal
356Recursive Type Aliases
357Type Aliases vs Inline Types
358Extending Interfaces with extends
359Multiple Interface Extension
360Interface Extension vs Intersection Types
361Declaration Merging Basics
362Merging Properties in Interfaces
363Merging Function Overloads in Interfaces
364Declaration Merging with Modules
365Augmenting Third-Party Interfaces
366Declaration Merging Pitfalls
367Type Aliases Cannot Merge
368Hybrid Approaches: Interfaces + Type Aliases
369When to Leverage Declaration Merging
370The Equivalence: Interfaces and Types Often Do the Same Thing
371Declaration Merging: The Key Interface Superpower
372When Declaration Merging Is Desirable
373Unions and Intersections: Type Aliases Shine
374Primitive and Literal Types: Only Type Aliases Work
375Performance: Interfaces Check Faster in Some Cases
376Extends vs Intersection: Subtle Semantic Differences
377Error Messages: Interfaces Show Names, Types Show Shapes
378Community Conventions: Object Shapes Use Interfaces
379Computed Properties: Type Aliases Are More Flexible
380Consistency Within a Codebase Matters Most
381Practical Decision Tree: When to Choose Which

338What Interfaces Are
339Basic Interface Syntax
340Interface vs Object Type Literal
341Optional Properties in Interfaces
342Readonly Properties in Interfaces
343Method Signatures in Interfaces
344Index Signatures in Interfaces
345Implementing Interfaces with Classes
346Multiple Interface Implementation
347Interfaces for Function Types
348What Is a Type Alias?
349Basic Type Alias Syntax
350Aliasing Primitive and Literal Types
351Aliasing Object Types
352Aliasing Function Types
353Aliasing Union Types
354Aliasing Intersection Types
355Type Aliases Are Not Nominal
356Recursive Type Aliases
357Type Aliases vs Inline Types
358Extending Interfaces with extends
359Multiple Interface Extension
360Interface Extension vs Intersection Types
361Declaration Merging Basics
362Merging Properties in Interfaces
363Merging Function Overloads in Interfaces
364Declaration Merging with Modules
365Augmenting Third-Party Interfaces
366Declaration Merging Pitfalls
367Type Aliases Cannot Merge
368Hybrid Approaches: Interfaces + Type Aliases
369When to Leverage Declaration Merging
370The Equivalence: Interfaces and Types Often Do the Same Thing
371Declaration Merging: The Key Interface Superpower
372When Declaration Merging Is Desirable
373Unions and Intersections: Type Aliases Shine
374Primitive and Literal Types: Only Type Aliases Work
375Performance: Interfaces Check Faster in Some Cases
376Extends vs Intersection: Subtle Semantic Differences
377Error Messages: Interfaces Show Names, Types Show Shapes
378Community Conventions: Object Shapes Use Interfaces
379Computed Properties: Type Aliases Are More Flexible
380Consistency Within a Codebase Matters Most
381Practical Decision Tree: When to Choose Which

Lesson 371 of 1,796·8. Interfaces vs Type AliasesPro lesson

Declaration Merging: The Key Interface Superpower

Interfaces can be declared multiple times and automatically merge, enabling extensibility patterns impossible with type aliases.

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