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export and import

Learn ES module export and import.

export and import

With the export keyword you can export a variable, function, or type from a module. From another module you import these items with import { name } from "./path". The names inside curly braces must match the exported names exactly.

// matematik.ts
export function topla(a: number, b: number) {
  return a + b;
}

// app.ts
import { topla } from "./matematik";
console.log(topla(2, 3));  // 5

Multiple named exports

A module can have as many named exports as you want. Each export keyword adds a new export. When importing, you can take multiple items in a single import statement separated by commas: import { topla, cikar } from "./matematik".

Practice Call an exported function

Define topla as an exported function with signature (a: number, b: number): number returning a + b. Then print the result of topla(3, 4) with console.log.

Starter code

index.ts
// topla adında bir fonksiyonu dışa aktararak tanımla
// a ve b parametreleri alsın, toplamlarını döndürsün
// fonksiyonu 3 ve 4 ile çağırıp sonucu yazdır

Sample solution

index.ts
export function topla(a: number, b: number): number {
  return a + b;
}
console.log(topla(3, 4));

Expected output

7

Questions and answers

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

1 Which syntax is used to import a named-exported function?

  • import { topla } from "./matematik" Correct answer
  • import topla from "./matematik"
  • import * topla from "./matematik"
  • import [ topla ] from "./matematik"

Explanation: For a named export you give the name in curly braces: import { topla } from "./matematik". Writing without braces is for default exports; * requires as; square brackets are invalid.

2 Add export

Question 
____ function topla(a: number, b: number): number {
  return a + b;
}
Answer 
export function topla(a: number, b: number): number {
  return a + b;
}

Explanation: To export a function you write export at the start of its declaration. default is for a separate default export; public and static are for class members, not module exports.

3 export and import parts

Term Meaning
export function topla Named export declaration
import { topla } Import with curly braces
{ topla, cikar } Multiple names with commas
from "./matematik" Module path

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