TypeScript Basics for JavaScript Developers

TypeScript is a typed superset of JavaScript that compiles to plain JavaScript. It adds optional static typing, interfaces, and other features that make large codebases much more maintainable.

Basic Types

let name: string = 'Alice';
let age: number = 30;
let isActive: boolean = true;
let tags: string[] = ['ts', 'js'];

Interfaces

interface Post {
  id: number;
  title: string;
  content: string;
  published?: boolean; // optional
}

Functions

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

const add = (a: number, b: number): number => a + b;

Generics

function first<T>(arr: T[]): T {
  return arr[0];
}

const num = first([1, 2, 3]);    // type: number
const str = first(['a', 'b']);   // type: string