TypeScript6 exercises

TypeScript Interface vs Type: When to Use Each

Practice choosing between TypeScript interfaces and type aliases. Covers extends, declaration merging, unions, and composition patterns.

Warm-up1 / 1

Can you write this from memory?

Create Admin interface extending User with role: string

In TypeScript, both interface and type can define object shapes, but they're not interchangeable. Interfaces support declaration merging and extends. Types handle unions, tuples, and mapped types.

This page covers the decision points. For a side-by-side comparison with a quick decision table, see the interfaces vs types cheat sheet.

What You'll Practice: TypeScript Interface vs Type: When to Use Each

Choose between interface and type for object shapesExtend interfaces with extendsCompose types with intersection (&)Use declaration merging for library augmentationRecognize TS 5 behavior differences

TypeScript Interface vs Type: When to Use Each Sample Exercises

Example 1Difficulty: 1/5

Fill in the type for the name property (it holds text)

string

Example 2Difficulty: 1/5

Fill in the return type for the greet method

string

Example 3Difficulty: 2/5

Fill in the character to make the email property optional

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Quick Reference

TypeScript Interface vs Type: When to Use Each Cheat Sheet →

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