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Question model

Design question, option, and answer types.

What is a question model?

In a quiz app, the question model is designed first. A question consists of text, options, and the index of the correct answer. In TypeScript you define this structure with an interface. This way all questions share the same shape and missing fields are caught at compile time.

interface Question {
  text: string;
  options: string[];
  correctIndex: number;
}

Answer and option types

Beside the question model, answer and option types are also defined. Options are a string[] array; the user's answer is the index of the chosen option, i.e. a number. This separation keeps each part of the model with a single responsibility.

type Answer = number;  // chosen option index
type Option = string;   // an option text

Practice Create a question object

Define a Soru interface: metin: string, siklar: string[], dogruIndex: number. Create a Soru object named s1 with text "TS nedir?", options ["dil", "renk", "araç"], and correct index 0. Print s1.metin with console.log.

Starter code

index.ts
// Soru interface tanımla
// s1 adında bir Soru nesnesi oluştur
// s1.metin yazdır

Sample solution

index.ts
interface Soru {
  metin: string;
  siklar: string[];
  dogruIndex: number;
}
const s1: Soru = {
  metin: "TS nedir?",
  siklar: ["dil", "renk", "araç"],
  dogruIndex: 0
};
console.log(s1.metin);

Expected output

TS nedir?

Questions and answers

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

1 What type should the dogruIndex field be in a Soru interface?

  • number Correct answer
  • string
  • boolean
  • string[]

Explanation: Since the index of the correct answer is a number, the dogruIndex field is defined as number.

2 Question interface keyword

Question 
 ____ Soru {
  metin: string;
  siklar: string[];
  dogruIndex: number;
}
Answer 
 interface Soru {
  metin: string;
  siklar: string[];
  dogruIndex: number;
}

Explanation: The interface keyword is used to define an object structure; type alias is an alternative but interface is more suitable for objects.

3 Question model parts

Term Meaning
metin Question text
siklar Options array
dogruIndex Correct answer index
Cevap Chosen option number

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