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Challenge 2: Generics

Solve a task using generics and constraints.

Generics challenge

In this challenge you will solve tasks that combine generic functions and constraints. You learned to define type parameters with <T>, add constraints with extends, and use keys with keyof. Generics preserve type safety while allowing code to work with any type.

Practice uzunluk generic function

Define a generic function named uzunluk: <T extends { length: number }>(x: T): number. Its body should be return x.length. Print the result of calling uzunluk("merhaba") with console.log.

Starter code

index.ts
// uzunluk adinda generic fonksiyon
// T parametresi length ozelligi olanlarla sinirli
// x.length degerini dondur
// "merhaba" ile cagir

Sample solution

index.ts
function uzunluk<T extends { length: number }>(x: T): number {
  return x.length;
}
console.log(uzunluk("merhaba"));

Expected output

7

Practice Field access with keyof

Define a generic function named al: <T, K extends keyof T>(obj: T, anahtar: K): T[K]. Its body should be return obj[anahtar]. The kisi object is { ad: "Ayşe", yas: 30 }. Print the result of calling al(kisi, "ad") with console.log.

Starter code

index.ts
// al adinda generic fonksiyon
// iki tür parametresi T ve K
// K T'nin anahtarlarindan biri olsun
// obj[anahtar] degerini dondur
// kisi nesnesi tanimla
// al ile "ad" al ve yazdir

Sample solution

index.ts
function al<T, K extends keyof T>(obj: T, anahtar: K): T[K] {
  return obj[anahtar];
}
const kisi = { ad: "Ayşe", yas: 30 };
console.log(al(kisi, "ad"));

Expected output

Ayşe

Questions and answers

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

1 What is used to require a generic type parameter to have a specific structure?

  • readonly
  • implements
  • abstract
  • extends constraint Correct answer

Explanation: The extends constraint requires the type parameter to have a specific structure or type; for example <T extends { length: number }>.

2 extends constraint

Question 
function uzunluk<T ____ { length: number }>(x: T): number {
  return x.length;
}
Answer 
function uzunluk<T extends { length: number }>(x: T): number {
  return x.length;
}

Explanation: The extends keyword is used for generic constraints; implements is for classes, keyof is for keys.

3 Generic concepts

Term Meaning
<T> Type parameter
extends Constraint
keyof Key set
default Default type

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