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number type

Learn to define numbers with the number type.

What is the number type?

The number type holds both integers and decimals; TypeScript has no separate int or float type. The type annotation again uses a colon.

let yas: number = 25;
let fiyat: number = 19.99;
console.log(yas, fiyat);  // 25 19.99

Whether you write 5 or 5.5, both are accepted as number.

Arithmetic with number

You can perform addition (+), subtraction (-), multiplication (*) and division (/) on number values. The result is again of type number.

let a: number = 12;
let b: number = 4;
console.log(a + b);  // 16
console.log(a / b);  // 3

Practice Declare two numbers and print them

Declare a number variable named yas with value 30. Declare a second number named boy with value 1.75. Print both with a single console.log.

Starter code

index.ts
// yas ve boy adında iki number değişken tanımla

// ikisini tek console.log ile yazdır

Sample solution

index.ts
let yas: number = 30;
let boy: number = 1.75;
console.log(yas, boy);

Expected output

30 1.75

Questions and answers

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

1 Which of the following assignments is valid?

  • let fiyat: number = "19.99";
  • let fiyat: int = 19.99;
  • let fiyat: float = 19.99;
  • let fiyat: number = 19.99; Correct answer

Explanation: TypeScript uses the single number type for both integers and decimals; there is no int or float. A text value cannot be assigned to number.

2 Complete the type annotation

Question 
let sicaklik: ____ = 23.5;
Answer 
let sicaklik: number = 23.5;

Explanation: TypeScript has no separate type for integers and decimals; both use number.

3 number concepts

Term Meaning
number integer and decimal type
25 integer value
19.99 decimal value
: number type name

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