Interface vs type alias

Learn the difference between Interface and type alias.

Interface vs type alias

Both interface and type can define object shapes. interface is specifically for objects and can be extended. type is more general; it can also define unions and primitives.

// interface
interface Kisi { ad: string; yas: number; }
// type alias
type Nokta = { x: number; y: number };

Both can be used for simple object shapes.

When to use interface and type?

interface is preferred for object shapes that may be extended. type is used for union types, intersection types, or primitive aliases. Both work for object shapes.

// interface can be extended
interface Hayvan { ad: string }
interface Kedi extends Hayvan { miyav: string }

Choose interface or type based on the need.

Exercise Interface and type alias together

Define an interface named Kisi with properties ad: string and yas: number. Define a type alias named Nokta ({ x: number; y: number }). Declare a variable named kisi of type Kisi with value { ad: "Veli", yas: 30 }. Print the value of kisi.ad with console.log.

Show example solution

interface Kisi {
    ad: string;
    yas: number;
}
type Nokta = { x: number; y: number };
let kisi: Kisi = { ad: "Veli", yas: 30 };
console.log(kisi.ad);

Test yourself

Which is specifically designed for object shapes?
- type
- const
- interface
- let
Show answer

interface — The <code>interface</code> keyword is specifically designed for defining object shapes; <code>type</code> is more general and can also define union types.

Add the correct keyword

____ Kisi { ad: string; yas: number; }

Show answer

interface Kisi { ad: string; yas: number; }

Interface vs type concepts

interface X { ... }

Specific for object shapes
type X = { ... }

General type definition
type X = string | number

Union type (type only)
interface vs type

Interface is specific to objects

Next lesson: Summary - Interfaces

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