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Summary - Objects

Write a user card by combining object types.

Summary - Objects

Object types let you model data precisely: shape defines properties, ? marks optional properties, and readonly marks immutable properties. Together they create safe and clear data structures.

let kullanici: {
  readonly id: number;
  ad: string;
  eposta?: string
} = { id: 1, ad: "Ali" };

These three features together create flexible but safe object types.

Practice Write a user card

Declare a variable named kullanici with type { readonly id: number; ad: string; eposta?: string } and value { id: 1, ad: "Zeynep", eposta: "z@x.com" }. Print the value of kullanici.eposta with console.log.

Starter code

index.ts
// kullanici adında bir nesne tanımla
// id özelliği readonly sayı, ad özelliği zorunlu dize, eposta özelliği isteğe bağlı dize olsun
// id değeri 1, ad değeri "Zeynep", eposta değeri "z@x.com" olsun
// kullanici.eposta değerini yazdır

Sample solution

index.ts
let kullanici: { readonly id: number; ad: string; eposta?: string } = { id: 1, ad: "Zeynep", eposta: "z@x.com" };
console.log(kullanici.eposta);

Expected output

z@x.com

Questions and answers

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

1 Which type allows the value <code>{ ad: "Ali" }</code> but prevents reassigning <code>ad</code>?

  • { readonly ad: string } Correct answer
  • { ad: string; tel?: string }
  • { readonly id: number; ad: string }
  • { ad?: string }

Explanation: <code>{ readonly ad: string }</code> makes <code>ad</code> both required and immutable; the value <code>{ ad: "Ali" }</code> is valid and <code>ad</code> cannot be changed later.

2 Complete the optional property type

Question 
let kullanici: { readonly id: number; ad: string; eposta?: ____ } = { id: 1, ad: "Ali" };
Answer 
let kullanici: { readonly id: number; ad: string; eposta?: string } = { id: 1, ad: "Ali" };

Explanation: Since <code>eposta</code> is an email address, its type must be <code>string</code>; <code>number</code> and <code>boolean</code> are wrong types for an email, and <code>void</code> is not a property type.

3 Object concepts summary

Term Meaning
{ ad: string } Required property
tel?: string Optional property
readonly id: number Immutable property
Object type Object shape

All lessons in Beginner

1 TypeScript intro and setup

  1. What is TypeScript?
  2. Why TypeScript?
  3. tsc compiler
  4. tsconfig basics
  5. Summary - TypeScript basics

2 Primitive types

  1. string type
  2. number type
  3. boolean type
  4. let and const
  5. Summary - Primitive types

3 Arrays

  1. Array type
  2. Array methods
  3. readonly arrays
  4. Multidimensional arrays
  5. Summary - Arrays

4 Tuples

  1. What is a tuple?
  2. Tuple usage
  3. readonly tuple
  4. Summary - Tuple

5 Enums

  1. Numeric enum
  2. String enum
  3. const enum
  4. Enum members
  5. Summary - Enum

6 any, unknown, never

  1. any type
  2. unknown type
  3. never type
  4. void type
  5. Summary - Special types

7 Type annotation

  1. Variable annotation
  2. Parameter annotation
  3. Return type annotation
  4. Summary - Type annotation

8 Type inference

  1. Basic inference
  2. Inference with const
  3. Best common type
  4. Summary - Type inference

9 Objects

  1. Object type
  2. Optional properties
  3. Readonly properties
  4. Summary - Objects

10 Functions

  1. Function declaration
  2. Optional and default params
  3. Rest params
  4. Function overloads
  5. Summary - Functions

11 Arrow functions

  1. Arrow syntax
  2. this with arrow
  3. Arrow type
  4. Summary - Arrow functions

12 Interfaces

  1. What is an interface?
  2. Property types
  3. Interface vs type alias
  4. Summary - Interfaces

13 Type alias

  1. What is a type alias?
  2. Composition with alias
  3. Alias vs interface
  4. Summary - Type alias

14 Union and intersection

  1. Union types
  2. Intersection types
  3. Literal types
  4. Summary - Union & intersection

15 null and undefined

  1. null vs undefined
  2. Optional chaining
  3. Nullish coalescing
  4. Summary - null & undefined

16 Strict mode

  1. strict: true
  2. strictNullChecks
  3. strictFunctionTypes
  4. Summary - Strict mode

17 Project: Shopping cart

  1. Cart design
  2. Add product
  3. Total calculation
  4. Apply discount
  5. Integration

18 Project: Todo CLI

  1. Task model
  2. Add and list
  3. Completion
  4. Filtering
  5. Integration

19 Project: Library

  1. Book model
  2. Add and search
  3. Borrow
  4. Return
  5. Integration

20 Beginner final

  1. Challenge 1: Types
  2. Challenge 2: Functions
  3. Challenge 3: Unions
  4. Challenge 4: Mini app