Basic Types

TypeScript Type System•Section 2 of 4•beginner

Topic Overview

Take your time to understand each concept. Practice with the examples below!

TypeScript has a rich type system with many different types to choose from. Let's explore each one with real-world examples!

Primitive Types - The Building Blocks:

•
string:Text data like names, messages, or any text
•
number:All numbers - integers, decimals, negative numbers
•
boolean:True or false values for yes/no decisions
•
symbol:Unique identifiers (advanced use)
•
bigint:Really large numbers (beyond regular number limits)

Arrays - Lists of Things:

•
Basic array:number[] for a list of numbers
•
Alternative syntax:Array<string> for a list of strings
•
Mixed arrays:(string | number)[] can contain both
•
Readonly arrays:readonly string[] can't be modified

Tuples - Fixed-Length Arrays:

Think of tuples as a shopping list where order and count matter:

•
Coordinates:[x: number, y: number]
•
User info:[name: string, age: number, isActive: boolean]
•Fixed length and types in specific positions

Enums - Named Constants:

Perfect for a fixed set of values like days of the week or user roles:

•
Numeric enums:enum Days { Monday, Tuesday, Wednesday }
•
String enums:enum Colors { Red = "RED", Blue = "BLUE" }
•Makes code more readable and prevents typos

Special Types:

•
any:The escape hatch - accepts any type (use sparingly!)
•
unknown:Safer than any - must check type before use
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void:Functions that don't return anything
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never:Functions that never return (throw errors or infinite loops)
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null and undefined:Absence of value

Object Types:

•
Basic objects:{ name: string; age: number }
•
Optional properties:{ name: string; age?: number }
•
Index signatures:{ [key: string]: any } for dynamic keys

Example

// Primitive Types
let message: string = "Hello TypeScript";
let count: number = 42;
let pi: number = 3.14159;
let isComplete: boolean = true;
// Arrays
let numbers: number[] = [1, 2, 3, 4, 5];
let colors: Array<string> = ["red", "green", "blue"];
let mixed: (string | number)[] = ["Alice", 25, "Bob", 30];
// Tuples - fixed length arrays with specific types
let person: [string, number] = ["Alice", 30];
let coordinate: [number, number, number] = [10, 20, 30];
// Enums
enum Direction {
  Up = "UP",
  Down = "DOWN",
  Left = "LEFT",
  Right = "RIGHT"
}
enum StatusCode {
  Success = 200,
  NotFound = 404,
  ServerError = 500
}
let userDirection: Direction = Direction.Up;
let responseStatus: StatusCode = StatusCode.Success;
// Special types
let uncertain: any = "could be anything";
let nothing: void = undefined;
let empty: null = null;
let notDefined: undefined = undefined;
console.log(`Direction: ${userDirection}, Status: ${responseStatus}`);

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