The Complete Guide to TypeScript¶

TypeScript is JavaScript with types. And that changes everything.

Why TypeScript¶

• Catch errors at compile time, not in production
• Better IDE support (autocomplete, refactoring)
• Documentation in code
• Safer refactoring

Basic Types¶

let name: string = “TypeScript”; let version: number = 5.3; let active: boolean = true; let items: string[] = [“a”, “b”]; let tuple: [string, number] = [“age”, 30];

Interfaces & Types¶

interface User { id: number; name: string; email?: string; // optional readonly createdAt: Date; }

type Status = “active” | “inactive” | “banned”;

Generics¶

function first(arr: T[]): T | undefined { return arr[0]; }

interface ApiResponse { data: T; error?: string; }

Utility Types¶

Partial // all properties optional Required // all required Pick Omit Record

Enums vs Union Types¶

// Prefer union types type Direction = “north” | “south” | “east” | “west”;

// Enum only when you need runtime values enum HttpStatus { OK = 200, NotFound = 404 }

Strict Mode¶

// tsconfig.json { “compilerOptions”: { “strict”: true } } // Always! Without strict mode you lose half the benefits of TS.

Rule¶

Strict mode always on. Avoid “any”. If you do not know the type, use “unknown”.