TypeScript is a language for application scale JavaScript development
TypeScript is Microsoft's statically-typed superset of JavaScript that compiles to plain JavaScript. It adds optional type annotations, interfaces, and compile-time type checking to JavaScript, allowing developers to catch errors during development rather than at runtime. With over 116 million weekly downloads, TypeScript has become the de facto standard for building large-scale JavaScript applications.
The package includes the TypeScript compiler (tsc), language services for editor integration, and a comprehensive standard library with type definitions. TypeScript code is valid JavaScript plus type annotations, meaning you can adopt it gradually—rename .js files to .ts and add types incrementally. The compiler strips out all type information during compilation, producing clean, readable JavaScript that runs anywhere JavaScript runs.
Major frameworks and libraries including Angular, Vue 3, NestJS, and countless others are built with TypeScript. The language is maintained by Microsoft and has evolved to include advanced type system features like conditional types, template literal types, and robust type inference. The @types ecosystem on npm provides type definitions for virtually every popular JavaScript library, enabling type-safe integration even with packages not written in TypeScript.
// user.ts - Define interfaces and types
interface User {
id: number;
email: string;
role: 'admin' | 'user' | 'guest';
metadata?: Record<string, unknown>;
}
// Type-safe function with error handling
async function fetchUser(userId: number): Promise<User> {
const response = await fetch(`https://api.example.com/users/${userId}`);
if (!response.ok) {
throw new Error(`Failed to fetch user: ${response.status}`);
}
const data: User = await response.json();
return data;
}
// Generic utility function with type constraints
function filterByRole<T extends User>(users: T[], role: User['role']): T[] {
return users.filter(user => user.role === role);
}
// Usage with full type inference
async function main() {
const user = await fetchUser(123);
console.log(user.email.toUpperCase()); // IDE knows email is string
const users: User[] = [
{ id: 1, email: 'admin@example.com', role: 'admin' },
{ id: 2, email: 'user@example.com', role: 'user' }
];
const admins = filterByRole(users, 'admin');
// Type error caught at compile time:
// const invalid = filterByRole(users, 'superuser');
}
main();Large-scale application development: Teams building complex applications use TypeScript to maintain code quality across dozens or hundreds of developers. The type system catches integration errors, documents expected data shapes, and enables safe refactoring.
API client and SDK development: TypeScript excels at modeling API responses, request payloads, and service contracts. Type definitions serve as living documentation and prevent runtime errors from malformed data.
Node.js backend services: Server-side applications benefit from TypeScript's ability to model database schemas, validate request/response types, and provide IDE autocomplete for business logic across multiple modules.
Library and package authoring: Publishing TypeScript packages with generated .d.ts declaration files gives consumers first-class editor support, autocompletion, and inline documentation without requiring them to use TypeScript.
Legacy JavaScript codebase migration: Teams can incrementally adopt TypeScript by converting files one at a time, adding type safety to critical paths while leaving low-risk code as JavaScript.
npm install typescriptpnpm add typescriptbun add typescript