Type vs Interface in TypeScript: Clear Differences and When to Use Each

When working with TypeScript, you often define the structure of data using types and interfaces. While they seem similar, understanding their differences and knowing when to use each is key for clean, scalable code.

What are Types and Interfaces ?

Interface: Mainly used to describe the shape of objects. They support declaration merging, meaning you can extend them by declaring the same interface multiple times.

Type: A more flexible tool that can represent object shapes, primitives, unions, intersections, and tuples. Types can't be re-opened or merged once declared.

Difference between Interface and Type

Feature	TypeScript Interface	TypeScript Type
Purpose	Defines shape of objects/classes	Defines objects, primitives, unions, intersections
Extensibility	Supports declaration merging & extends keyword	Can create intersections (&) but no declaration merging
Primitive Types	Can’t describe primitives	Can alias primitives like string, number, boolean
Union / Intersection	Supports extending but no union/intersection types	Supports union ( | ) and intersection ( & ) types
Use Case	Best for public APIs & extensible object shapes	Best for flexible type aliases, complex compositions

Real-Time Scenario: Defining User Profiles

Imagine you’re building a social app with user profiles.

Using Interface:

Here, interfaces let you extend UserProfile seamlessly, useful when APIs evolve or third-party types need augmentation.

Using Type:

Types allow you to combine multiple shapes using intersections, great for complex data structures involving unions or tuples.

When to Choose Which?

Choose Interface: When designing public APIs or object models that might need extension or merging.

Choose Type: For more complex type compositions like unions, tuples, or primitives where flexibility is needed.

Conclusion

Both types and interfaces are powerful. Use interfaces for clear object shapes and extendability, and types for flexibility with complex data. Mastering both helps write robust TypeScript code tailored to your project needs.