Interfaces

Intro to Interfaces
Intro to Interfaces
Interfaces are another way to define object shapes in TypeScript. They're similar to type aliases for objects, but with some key differences.
interface User {
	name: string
	email: string
}

const user: User = { name: 'Alice', email: 'alice@example.com' }

Interface vs Type Alias

Both can define object shapes:
// Type alias
type User = { name: string; email: string }

// Interface
interface User {
	name: string
	email: string
}
Key differences:
FeatureType AliasInterface
Object shapes✅✅
Union types✅❌
Declaration merging❌✅
Extends keywordUse &extends
Class implementation✅✅ (preferred)

When to Use Interfaces

  • Object shapes that may be extended
  • Class contracts (implements)
  • Library APIs that users might extend
  • When you prefer the extends syntax
Many teams choose one and stick with it. The most common convention is: interfaces for objects, type aliases for everything else.
In this exercise, you'll work with interfaces and their unique features.
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