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Array type

Learn to define arrays and specify their types.

Array type

In TypeScript, an array is an ordered list of values of the same type. The array type is written in two ways: number[] or Array<number>. The type inside the brackets specifies the type of elements the array holds. The type annotation comes after the variable with :.

let sayilar: number[] = [1, 2, 3];
let isimler: Array<string> = ["Ali", "Ayşe"];

Type checking and inference

When you specify a type for an array, TypeScript prevents adding wrong-typed elements. Even without a type annotation, TypeScript infers the array type from the initial assignment. Writing the explicit type is safer.

let renkler: string[] = ["kırmızı", "mavi"];
renkler.push("yeşil");
// renkler.push(5); // Error

Practice Prices array

Define a number[] array named fiyatlar with the values 100, 250, 75. Then print the array with console.log.

Starter code

index.ts
// fiyatlar dizisini number[] türüyle tanımla ve yazdır

Sample solution

index.ts
let fiyatlar: number[] = [100, 250, 75];
console.log(fiyatlar);

Expected output

[ 100, 250, 75 ]

Questions and answers

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

1 What does the `Array<number>` notation specify?

  • All elements of the array being of number type Correct answer
  • Elements of the array being of different types
  • The array holding only a single number
  • The array always starting empty

Explanation: The `Array<number>` notation requires every element of the array to be of type `number`; adding a different type gives a compile error.

2 Specify an array type

Question 
let notlar: number____ = [70, 85, 90];
Answer 
let notlar: number[] = [70, 85, 90];

Explanation: The `number[]` notation specifies an array type of `number` elements; so two square brackets are needed in the blank.

3 Array type notations

Term Meaning
number[] Short notation for a number array
Array<string> General notation for a string array
boolean[] Short notation for a boolean array
Array<number> General notation for a number array

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