TypeScript to JavaScript Converter Free Online Tool 2026

Last updated March 22, 2026

TypeScript to JavaScript Converter Examples

The TypeScript to JavaScript Converter removes type annotations and TypeScript-specific syntax, producing plain JavaScript. Below are practical examples showing what each TypeScript construct compiles to.

Type Annotations Removed

// TypeScript
const name: string = "Alice";
const age: number = 30;
const active: boolean = true;
let items: string[] = [];
let count: number | null = null;

// JavaScript (types removed)
const name = "Alice";
const age = 30;
const active = true;
let items = [];
let count = null;

Function Type Annotations

// TypeScript
function greet(name: string, greeting: string = "Hello"): string {
  return `${greeting}, ${name}!`;
}

async function fetchUser(id: number): Promise<User> {
  const response = await fetch(`/api/users/${id}`);
  return response.json();
}

// JavaScript (types removed)
function greet(name, greeting = "Hello") {
  return `${greeting}, ${name}!`;
}

async function fetchUser(id) {
  const response = await fetch(`/api/users/${id}`);
  return response.json();
}

Interface Removal

// TypeScript
interface User {
  id: number;
  name: string;
  email: string;
  role: 'admin' | 'user';
  createdAt: Date;
}

interface ApiResponse<T> {
  data: T;
  status: number;
  message: string;
}

function createUser(user: User): ApiResponse<User> {
  return { data: user, status: 201, message: 'Created' };
}

// JavaScript (interfaces completely removed)
function createUser(user) {
  return { data: user, status: 201, message: 'Created' };
}

Type Alias Removal

// TypeScript
type UserId = number;
type Status = 'active' | 'inactive' | 'pending';
type Callback<T> = (error: Error | null, result: T) => void;

function getUser(id: UserId): Status {
  return 'active';
}

// JavaScript (type aliases removed)
function getUser(id) {
  return 'active';
}

Generic Functions

// TypeScript
function identity<T>(value: T): T {
  return value;
}

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

function merge<T, U>(obj1: T, obj2: U): T & U {
  return { ...obj1, ...obj2 };
}

// JavaScript (generic type parameters removed)
function identity(value) {
  return value;
}

function first(arr) {
  return arr[0];
}

function merge(obj1, obj2) {
  return { ...obj1, ...obj2 };
}

Class with Access Modifiers

// TypeScript
class UserService {
  private readonly db: Database;
  protected logger: Logger;
  public name: string;

  constructor(db: Database, logger: Logger) {
    this.db = db;
    this.logger = logger;
    this.name = 'UserService';
  }

  public async findById(id: number): Promise<User | null> {
    return this.db.query<User>(`SELECT * FROM users WHERE id = ?`, [id]);
  }

  private validateId(id: number): boolean {
    return id > 0;
  }
}

// JavaScript (access modifiers removed)
class UserService {
  constructor(db, logger) {
    this.db = db;
    this.logger = logger;
    this.name = 'UserService';
  }

  async findById(id) {
    return this.db.query(`SELECT * FROM users WHERE id = ?`, [id]);
  }

  validateId(id) {
    return id > 0;
  }
}

Enum Conversion

// TypeScript
enum Direction {
  Up = 'UP',
  Down = 'DOWN',
  Left = 'LEFT',
  Right = 'RIGHT'
}

enum Status {
  Active = 1,
  Inactive = 2,
  Pending = 3
}

// JavaScript (enums → objects)
const Direction = {
  Up: 'UP',
  Down: 'DOWN',
  Left: 'LEFT',
  Right: 'RIGHT'
};

const Status = {
  Active: 1,
  Inactive: 2,
  Pending: 3
};

Type Assertions

// TypeScript
const input = document.getElementById('name') as HTMLInputElement;
const value = (someValue as string).toUpperCase();
const num = <number>someValue;

// JavaScript (type assertions removed)
const input = document.getElementById('name');
const value = someValue.toUpperCase();
const num = someValue;

Optional Chaining and Nullish Coalescing

// TypeScript (ES2020+ features — preserved in modern JS output)
const city = user?.address?.city;
const name = user?.name ?? 'Anonymous';
const length = arr?.length ?? 0;

// JavaScript (ES2020+ — preserved as-is)
const city = user?.address?.city;
const name = user?.name ?? 'Anonymous';
const length = arr?.length ?? 0;

// JavaScript (ES5 target — compiled to older syntax)
const city = user === null || user === void 0
  ? void 0
  : (_a = user.address) === null || _a === void 0
  ? void 0
  : _a.city;
const name = (user === null || user === void 0 ? void 0 : user.name) !== null
  && (user === null || user === void 0 ? void 0 : user.name) !== void 0
  ? user.name : 'Anonymous';

Decorators

// TypeScript (with decorators)
@Injectable()
@Controller('/users')
class UserController {
  @Get('/:id')
  async getUser(@Param('id') id: string): Promise<User> {
    return this.userService.findById(parseInt(id));
  }
}

// JavaScript (decorators compiled)
let UserController = class UserController {
  async getUser(id) {
    return this.userService.findById(parseInt(id));
  }
};
UserController = __decorate([
  Injectable(),
  Controller('/users')
], UserController);
__decorate([
  Get('/:id'),
  __param(0, Param('id'))
], UserController.prototype, "getUser", null);

React Component (TSX → JSX)

// TypeScript (TSX)
interface ButtonProps {
  label: string;
  onClick: () => void;
  disabled?: boolean;
  variant?: 'primary' | 'secondary';
}

const Button: React.FC<ButtonProps> = ({
  label,
  onClick,
  disabled = false,
  variant = 'primary'
}) => {
  return (
    <button
      className={`btn btn-${variant}`}
      onClick={onClick}
      disabled={disabled}
    >
      {label}
    </button>
  );
};

// JavaScript (JSX — types removed)
const Button = ({
  label,
  onClick,
  disabled = false,
  variant = 'primary'
}) => {
  return (
    <button
      className={`btn btn-${variant}`}
      onClick={onClick}
      disabled={disabled}
    >
      {label}
    </button>
  );
};

Common Use Cases

• Understand what JavaScript your TypeScript compiles to
• Debug type-related issues by seeing the runtime code
• Migrate TypeScript code to JavaScript environments
• Learn TypeScript by comparing TS and JS side by side
• Verify that TypeScript features compile correctly
• Prepare TypeScript snippets for JavaScript-only environments

Paste your TypeScript code into the converter and instantly see the equivalent JavaScript output.