TypeScript Cheat Sheet: Essential Code Examples

Rudrodip Sarker

Rudrodip Sarker

@rds_agi

TypeScript Cheat Sheet: Essential Code Examples

TypeScript Cheat Sheet: Essential Code Examples

TypeScript is a powerful superset of JavaScript that brings static typing and advanced features to your code. This cheat sheet provides a compilation of essential code snippets for common TypeScript concepts, making it a valuable reference for developers looking to enhance their coding skills.

Basic Types

Number

let age: number = 30;

String

let message: string = 'Hello, TypeScript!';

Boolean

let isActive: boolean = true;

Type Annotations

Function Parameter

function greet(name: string): string {
  return `Hello, ${name}!`;
}

Object Property

interface Person {
  firstName: string;
  lastName: string;
}
 
function getFullName(person: Person): string {
  return `${person.firstName} ${person.lastName}`;
}

Interfaces and Classes

Interface

interface Shape {
  area(): number;
}
 
class Circle implements Shape {
  constructor(private radius: number) {}
 
  area(): number {
    return Math.PI * this.radius * this.radius;
  }
}

Class Inheritance

class Rectangle extends Shape {
  constructor(private width: number, private height: number) {
    super();
  }
 
  area(): number {
    return this.width * this.height;
  }
}

Enums

enum Color {
  Red,
  Green,
  Blue
}
 
let selectedColor: Color = Color.Green;

Generics

function toArray<T>(arg: T): T[] {
  return [arg];
}
 
let stringArray: string[] = toArray('Hello');

Type Assertion

let value: any = 'TypeScript';
let length: number = (value as string).length;

Union and Intersection Types

Union Type

let value: string | number;
value = 'Hello';
value = 42;

Intersection Type

interface Employee {
  id: number;
  name: string;
}
 
interface Department {
  departmentId: number;
  departmentName: string;
}
 
let employee: Employee & Department;

Enums and String Enums

Numeric Enum

enum Direction {
  Up,
  Down,
  Left,
  Right
}

String Enum

enum HttpStatus {
  Ok = '200 OK',
  NotFound = '404 Not Found',
  InternalServerError = '500 Internal Server Error'
}

Modules and Namespace

Export and Import

// math.ts
export function add(a: number, b: number): number {
  return a + b;
}
 
// app.ts
import { add } from './math';

Namespace

namespace Geometry {
  export function area(radius: number): number {
    return Math.PI * radius * radius;
  }
}

Type Declarations

Type Definition

declare type Point = { x: number; y: number };

Ambient Declaration

declare module 'library' {
  export function greet(name: string): void;
}

Conclusion

This TypeScript cheat sheet covers a wide range of essential code snippets for common programming concepts. Whether you're dealing with basic types, type annotations, interfaces, classes, enums, generics, or module system, these snippets will serve as valuable references to help you master TypeScript and build robust applications with confidence.

See all blogs