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Type-only import

Learn type-only exports.

Type-only import

The import type syntax imports items that will be used only as types. These items do not exist at runtime; they are fully erased at compile time. Since they are removed from the generated JavaScript, the bundle size stays small.

// kisi.ts
export interface Kisi {
  ad: string;
}

// app.ts
import type { Kisi } from "./kisi";
function goster(k: Kisi) {
  return k.ad;
}

When to use type-only?

If you only need an interface, type alias, or type parameter from a module, you should use import type. This tells the compiler the item is not needed at runtime. Especially under isolatedModules, type-only items may be required to be imported with import type.

Practice Export a type and use it

Export interface Kisi with properties ad: string and yas: number. Export function goster with signature (k: Kisi): string and body return k.ad + k.yas. Print the result of goster({ ad: "Ece", yas: 25 }) with console.log.

Starter code

index.ts
// Kisi arayüzünü dışa aktar: ad string, yas number
// goster fonksiyonunu dışa aktar, Kisi parametreli
// ad ve yas değerlerini birleştirip döndürsün
// goster'i nesneyle çağır, sonucu yazdır

Sample solution

index.ts
export interface Kisi {
  ad: string;
  yas: number;
}

export function goster(k: Kisi): string {
  return k.ad + k.yas;
}

console.log(goster({ ad: "Ece", yas: 25 }));

Expected output

Ece25

Questions and answers

Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.

1 How can an item imported with <code>import type</code> be used?

  • Only in type positions Correct answer
  • Both as a type and as a value
  • Only as a value
  • Accessible at runtime

Explanation: An item imported with import type can only be used in type positions; it cannot be accessed as a value. It is fully erased at runtime, so value access is a compile error.

2 Add type

Question 
import ____ { Kisi } from "./kisi";
Answer 
import type { Kisi } from "./kisi";

Explanation: For a type-only import you write import type. only, interface, and as are not valid keywords in this position; only type carries this meaning.

3 Type-only import parts

Term Meaning
import type Type-only import
export interface Kisi Type export
from "./kisi" Module path
k: Kisi Type position usage

All lessons in Intermediate

1 Classes

  1. Class basics
  2. Constructor and fields
  3. Methods
  4. Static members
  5. Summary - Classes

2 Access modifiers

  1. public
  2. private
  3. protected
  4. Parameter properties
  5. Summary - Access modifiers

3 Readonly properties

  1. readonly fields
  2. Readonly parameter
  3. Readonly vs const
  4. Summary - Readonly

4 Generics

  1. What is a generic?
  2. Generic functions
  3. Generic classes
  4. Multiple type parameters
  5. Summary - Generics

5 Generic constraints

  1. extends constraint
  2. keyof constraint
  3. Default type parameter
  4. Summary - Generic constraints

6 Utility types

  1. Partial
  2. Required and Pick
  3. Omit and Record
  4. Summary - Utility types

7 keyof and typeof

  1. keyof operator
  2. typeof operator
  3. Indexing with keyof
  4. Summary - keyof and typeof

8 Mapped types

  1. What is a mapped type?
  2. Readonly mapped type
  3. Optional mapped type
  4. Summary - Mapped types

9 Conditional types

  1. What is a conditional type?
  2. Distributive conditional
  3. Logic with conditional
  4. Summary - Conditional types

10 infer

  1. infer keyword
  2. Extracting from Promise
  3. Array element type
  4. Summary - infer

11 Decorators

  1. What is a decorator?
  2. Method decorator
  3. Property decorator
  4. Decorator factories
  5. Summary - Decorators

12 Modules

  1. export and import
  2. Default export
  3. Re-export
  4. Type-only import
  5. Summary - Modules

13 Namespaces

  1. What is a namespace?
  2. Nested namespace
  3. Namespace vs module
  4. Summary - Namespaces

14 Declaration files

  1. What is .d.ts?
  2. Ambient module
  3. Triple-slash directive
  4. Summary - Declaration files

15 Advanced classes

  1. abstract class
  2. implements
  3. Get and set
  4. Summary - Advanced classes

16 Type assertion

  1. as keyword
  2. angle bracket syntax
  3. Type assertion vs casting
  4. Casting from unknown
  5. Summary - Type assertion

17 Project: Library package

  1. Package design
  2. Exporting types
  3. Generic helpers
  4. Declaration file
  5. Integration

18 Project: Quiz app

  1. Question model
  2. Question pool
  3. Answer check
  4. Score calculation
  5. Integration

19 Project: Weather app

  1. Weather model
  2. API response type
  3. Data transform
  4. Display
  5. Integration

20 Intermediate final

  1. Challenge 1: Classes
  2. Challenge 2: Generics
  3. Challenge 3: Type systems
  4. Challenge 4: Mini app