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Summary - Modules

Write a multi-file accounting package with modules.

Summary - Modules

Modules let you split and share code across files. Named exports give multiple items, default exports give a single default, re-exports create barrel files, and import type brings in type-only items. A module can hold both named and default exports, enabling flexible API design.

// hesap.ts
export interface Islem { a: number; b: number; }
export default function hesapla(i: Islem) {
  return i.a + i.b;
}

Practice Calculator package

Export interface Islem with properties a: number and b: number. Export hesapla as a default function with signature (i: Islem): number returning i.a + i.b. Print the result of hesapla({ a: 5, b: 7 }) with console.log.

Starter code

index.ts
// Islem arayüzünü dışa aktar: a ve b number
// hesapla fonksiyonunu varsayılan olarak dışa aktar
// Islem parametreli, a+b döndürsün
// hesapla'yı nesneyle çağır, sonucu yazdır

Sample solution

index.ts
export interface Islem {
  a: number;
  b: number;
}

export default function hesapla(i: Islem): number {
  return i.a + i.b;
}

console.log(hesapla({ a: 5, b: 7 }));

Expected output

12

Questions and answers

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

1 Can a module have both named and default exports at the same time?

  • Yes, both can coexist Correct answer
  • Only default export is allowed
  • Only named export is allowed
  • No, only one kind is used

Explanation: A module can have both named and default exports at the same time. Named exports are unlimited, the default export is single; together they offer a flexible API.

2 Default export

Question 
export ____ function hesapla(i: Islem): number {
  return i.a + i.b;
}
Answer 
export default function hesapla(i: Islem): number {
  return i.a + i.b;
}

Explanation: For a default export you write export default. named, single, and primary are not valid keywords; only default carries this meaning.

3 Match module concepts

Term Meaning
export function topla Named export
export default function Default export
export { } from Re-export
import type { } Type-only import

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