TypeScript for JavaScript Developers

TypeScript adds static type checking to JavaScript, helping you catch errors early and write more maintainable code.

Basic Type Annotations

Add type annotations to variables and functions:

typescript

// Variables
let name: string = 'John';
let age: number = 30;
let isActive: boolean = true;

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

// Arrays
let numbers: number[] = [1, 2, 3, 4, 5];
let names: string[] = ['Alice', 'Bob', 'Charlie'];

Interfaces

Define object shapes with interfaces:

typescript

interface User {
  id: number;
  name: string;
  email: string;
  isActive?: boolean; // Optional property
}

function createUser(userData: User): User {
  return {
    id: Date.now(),
    ...userData
  };
}