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Omit and Record

Learn Omit for removing and Record for mapping.

Omit and Record

Omit<T, K> removes from T the properties listed in K and keeps the rest. Record<K, V> builds an object type that stores a V value for every K key. Together they are handy for narrowing an interface and storing the result in a key-value table.

interface Urun { ad: string; fiyat: number; }
type Adetli = Omit<Urun, "fiyat">;
type Stok = Record<string, number>;

Mapping with Record

Record<K, V> is an object type where each key holds a value of the same type V. For example Record<string, number> maps city names to populations. For a fixed key set you can also use a union of keys like Record<"a" | "b", number>.

Practice Stock table

Define type Stok as Record<string, number>. Assign the object { elma: 5, armut: 3 } to a variable stoklar (of type Stok). Print stoklar.elma with console.log.

Starter code

index.ts
// Stok türünü her string anahtar number değer tutacak şekilde tanımla
// stoklar değişkenine { elma: 5, armut: 3 } ata, türü Stok olsun
// stoklar.elma'yı console.log ile yazdır

Sample solution

index.ts
type Stok = Record<string, number>;
const stoklar: Stok = { elma: 5, armut: 3 };
console.log(stoklar.elma);

Expected output

5

Questions and answers

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

1 What does <code>Omit&lt;Urun, "fiyat"&gt;</code> produce?

index.ts
interface Urun { ad: string; fiyat: number; }
type T = Omit<Urun, "fiyat">;
  • A type with all properties optional
  • A type with all properties required
  • A type with fiyat removed and the rest kept Correct answer
  • A type with only the fiyat property

Explanation: Omit removes the named properties and keeps the rest. Keeping only one is Pick, making optional is Partial, making required is Required.

2 Mapping type with Record

Question 
type Stok = ____<string, number>;
Answer 
type Stok = Record<string, number>;

Explanation: For a key-to-value mapping you use Record. Partial, Pick and Required serve other purposes and do not produce a mapping type.

3 Omit and Record parts

Term Meaning
Omit<T, K> Removes properties in K
Omit<Urun, "fiyat"> Type with fiyat removed
Record<K, V> Key-to-value mapping
Record<string, number> Each string key maps to a 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