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Required and Pick

Learn Required for required and Pick for selecting.

Required and Pick

Required<T> turns T's optional properties into required ones; it drops the ?. Pick<T, K> keeps only the properties of T listed in K and discards the rest. Together they narrow and tighten an interface.

interface Uye {
  ad: string;
  eposta?: string;
}
type ZorunluUye = Required<Uye>;
type SadeceAd = Pick<Uye, "ad">;

Required vs Partial

Required is the opposite of Partial. Fields left optional in an interface may become required for some functions. For example, if eposta is required at registration you use Required<Uye>. This lets you reuse the same base type at different strictness levels.

Practice Required member and summary

Define interface Uye with ad: string and eposta?: string. Write function kayit(u: Required<Uye>): void whose body prints the eposta via console.log(u.eposta). Call kayit({ ad: "Selin", eposta: "s@x.com" }).

Starter code

index.ts
// Uye arayüzünü ad: string ve eposta?: string ile tanımla
// kayit fonksiyonu parametresi Uye'nin zorunlu hali olsun
// gövdede console.log ile u.eposta yazdır
// ad ve eposta içeren nesneyle çağır

Sample solution

index.ts
interface Uye {
  ad: string;
  eposta?: string;
}
function kayit(u: Required<Uye>): void {
  console.log(u.eposta);
}
kayit({ ad: "Selin", eposta: "s@x.com" });

Expected output

s@x.com

Questions and answers

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

1 What does <code>Pick&lt;Uye, "ad" | "eposta"&gt;</code> produce?

index.ts
interface Uye { ad: string; eposta?: string; }
type T = Pick<Uye, "ad" | "eposta">;
  • A type with all properties optional
  • A type with ad and eposta removed
  • A type with all properties required
  • A type with only ad and eposta properties Correct answer

Explanation: Pick keeps the named properties and discards the rest. Optional is Partial, removal is Omit, required is Required.

2 Select properties with Pick

Question 
interface Urun { ad: string; fiyat: number; stok: number; }
type Ozet = ____<Urun, "ad" | "fiyat">;
Answer 
interface Urun { ad: string; fiyat: number; stok: number; }
type Ozet = Pick<Urun, "ad" | "fiyat">;

Explanation: To select specific properties you use Pick. Partial makes all optional; Required makes them required; Omit removes them.

3 Required and Pick parts

Term Meaning
Required<T> Makes optionals required
Pick<T, K> Selects properties in K
Pick<Uye, "ad"> Single property selection
Required<Uye> eposta becomes required

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