liminfoTypeScript Playground
Free web tool: TypeScript Playground
function greet(user) {
return `Hello, ${user.name}!`;
}
const users = [];
function findUser(id): User | undefined {
return users.find((u) => u.id === id);
}About TypeScript Playground
The TypeScript Playground is a free browser-based tool that strips TypeScript-specific syntax from your code to produce plain JavaScript. It handles the most common TypeScript constructs: interface and type declarations are removed entirely, type annotations on function parameters and return values are stripped, generic type parameters like `Array<User>` become bare `Array`, `as Type` cast expressions are removed, non-null assertion operators (`!.`) are cleaned up, `readonly` modifiers are deleted, and basic enum declarations are commented out with a warning.
This tool is useful for developers who want to quickly see what the JavaScript equivalent of a TypeScript snippet looks like, students learning which parts of TypeScript are type-erased at compile time, and engineers who need to paste TypeScript code into a plain JavaScript environment. The side-by-side layout shows your TypeScript input on the left and the JavaScript output on the right, updating in real time as you type.
The transformation is text-based using regex patterns rather than a full compiler AST, which means it handles the vast majority of common patterns accurately and instantly. A warnings panel below the output highlights constructs that were problematic or require special attention — for example, when an enum is encountered, a note advises replacing it with a const object for better runtime behavior. For production transpilation, the official TypeScript compiler or tools like esbuild and SWC are recommended.
Key Features
- Removes `interface` and `type` declarations (including exported ones) to produce clean JS output
- Strips type annotations from function parameters: `(id: number)` becomes `(id)`
- Removes function return type annotations: `(): string {` becomes `() {`
- Erases generic type parameters from calls and declarations: `Array<User>` becomes `Array`
- Removes `as Type` cast expressions that are TypeScript-only syntax
- Cleans up non-null assertion operators (`user!.name` becomes `user.name`)
- Deletes `readonly` modifiers from property and parameter declarations
- Warns about enum removals and suggests const object alternatives
Frequently Asked Questions
What TypeScript constructs does this playground handle?
It handles interface and type alias declarations, type annotations on variables and parameters, function return type annotations, generic type parameters on calls and declarations, `as Type` cast expressions, non-null assertion operators (`!`), `readonly` modifiers, and basic enum declarations. It covers the vast majority of everyday TypeScript patterns.
Is this the same as running `tsc --noEmit` or using Babel?
No. This is a text-based transformation using regular expressions, not a full compiler or AST transformer. It does not perform type checking, does not resolve imports, and does not handle all edge cases. For accurate, production-quality transpilation use the official TypeScript compiler (`tsc`), Babel with `@babel/preset-typescript`, esbuild, or SWC.
Why does the playground warn about enums?
TypeScript enums are a runtime construct — they generate real JavaScript objects, not just type information. Because their full transformation requires understanding the enum body structure and potentially preserving runtime values, this tool comments them out and suggests using a `const` object instead, which is idiomatic in modern TypeScript and transpiles to plain JS naturally.
Can I use this to learn what TypeScript erases at compile time?
Yes, that is one of its best use cases. TypeScript type erasure means that interfaces, type annotations, and generics disappear entirely in the compiled output. Seeing the before and after side by side is an effective way to understand which TypeScript features are purely compile-time constructs versus those that affect runtime behavior.
Why might the output not compile as valid JavaScript?
Because the transformation is regex-based, complex nested generics, conditional types, template literal types, or uncommon patterns may not be handled correctly. The tool notes in its UI that it is a basic transformation and edge cases may not be covered. Always verify the output before using it in production.
Does it handle TypeScript decorators?
No, decorator syntax (`@Injectable`, `@Component`, etc.) is not currently handled. Decorators are an advanced TypeScript/ECMAScript feature that requires AST-level transformation to process correctly. Use the official TypeScript compiler with `experimentalDecorators` enabled for decorator-heavy codebases.
Will it work on React TSX components?
Partially. The tool will strip type annotations and interfaces from TSX code. However, JSX syntax itself is not transformed — the output will still contain JSX tags. For full TSX-to-JS conversion including JSX transformation, use tsc, Babel, or esbuild.
Is my code sent to a server when I use this tool?
No. All transformation happens locally in your browser using JavaScript regex operations. Your TypeScript code is never uploaded to any server, stored in a database, or shared with third parties. The tool works entirely offline once the page is loaded.