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TypeScript Playground

Transpile TypeScript to JavaScript in your browser with configurable target and strict mode.

About TypeScript Playground

TypeScript Playground transpiles TypeScript 5 to JavaScript entirely in your browser, using the official TypeScript compiler loaded from jsDelivr CDN. There is nothing to install — on first use the compiler (~10 MB) loads once and is cached. Write TypeScript in the left editor, choose your JavaScript output target (ES5, ES2015, ES2020, or ESNext), toggle strict mode, and click Transpile to see the generated JavaScript in the right panel. Type-stripping uses ts.transpileModule, which is fast and produces clean output. Compiler diagnostics (type errors and warnings) are displayed below the editors when present. The tool is ideal for learning TypeScript, validating type syntax, quickly seeing how generics or decorators transpile, and checking what ES2020 optional chaining looks like after downlevelling to ES5.

Why use TypeScript Playground

  • Uses the official TypeScript 5.3 compiler, not a custom parser
  • Configurable target (ES5 through ESNext) for real downlevelling
  • Strict mode toggle shows how type-safe your code is
  • Compiler diagnostics surface type errors without requiring a build setup
  • Runs entirely in the browser — no Node.js or npm needed
  • Uses the official TypeScript 5.3 compiler, not a custom or partial parser, so output matches what tsc produces locally

How to use TypeScript Playground

  1. Paste TypeScript code into the left editor.
  2. Choose a JavaScript target version from the selector (ES5, ES2015, ES2020, ESNext).
  3. Toggle Strict mode and Remove comments as needed.
  4. Click Transpile — the TypeScript compiler loads on first use and runs the transpilation.
  5. Copy the JavaScript output from the right panel with the Copy JS button.
  6. Paste TypeScript code into the left editor — types, generics, interfaces, enums, and decorators are all accepted.
  7. Choose a JavaScript target version from the selector (ES5, ES2015, ES2020, ESNext) to control downlevelling.

When to use TypeScript Playground

  • Learning TypeScript and want to see what the compiled JS looks like
  • Checking whether TypeScript syntax is valid before adding it to a project
  • Demonstrating TypeScript features in a presentation or code review
  • Verifying how generics, decorators, or optional chaining downlevel to older JS
  • Quickly testing a TypeScript snippet without setting up a tsconfig
  • Learning TypeScript and want to see what the compiled JS looks like for each construct you try

Examples

Generic identity function

Input: function identity<T>(value: T): T { return value; } const n = identity<number>(42);

Output: function identity(value) { return value; } var n = identity(42);

Optional chaining (target ES5)

Input: const u: { name?: { first?: string } } = {}; const first = u.name?.first ?? 'unknown';

Output: var _a, _b; var u = {}; var first = (_b = (_a = u.name) === null || _a === void 0 ? void 0 : _a.first) !== null && _b !== void 0 ? _b : 'unknown';

Async function (target ES2020)

Input: async function fetchUser(id: number): Promise<{ id: number }> { return { id }; }

Output: async function fetchUser(id) { return { id }; }

Tips

  • ES5 target reveals how async/await becomes a state machine with regenerator-style helpers — useful for understanding bundler output.
  • Strict mode catches more type issues but does not enforce them at runtime — diagnostics are advisory in this tool.
  • Use 'as const' on object literals to see how TypeScript narrows tuple and union types in the JS output.
  • Decorator output requires experimentalDecorators in tsconfig — check the diagnostics if your decorators do not transpile.
  • Pin the target to ESNext when sharing modern code for Node 20+ environments to keep async/await native.
  • Comments are preserved unless you toggle Remove comments — handy for keeping JSDoc-style annotations in the output.
  • If a type error blocks output, ts.transpileModule still emits JS (types are erased) — diagnostics are non-blocking.

Frequently Asked Questions

Does this perform full type-checking?▾
No — it uses ts.transpileModule which strips types without full semantic analysis. Diagnostics shown are limited to what the single-file transpiler can detect.
Is my code sent to a server?▾
No. The TypeScript compiler runs entirely in your browser via the CDN-loaded typescript.js bundle. Your code never leaves your machine.
Which TypeScript version is used?▾
TypeScript 5.3.3, loaded from jsDelivr CDN on first use and cached by the browser for subsequent sessions.
What does the target selector control?▾
It sets the JS output version: ES5 for maximum compatibility, ES2020/ESNext for modern environments that support async/await, optional chaining, and nullish coalescing natively.
Can I use JSX or decorators?▾
JSX (TSX) is not enabled in the playground. Experimental decorators may work depending on the target selected, but are not explicitly configured.

Explore the category

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Glossary

Transpile
The process of converting source code from one language or version to another while preserving behaviour — here, TypeScript to JavaScript.
AST (Abstract Syntax Tree)
A tree representation of source code that the TypeScript compiler builds during parsing; transpilation walks and rewrites this tree.
ts.transpileModule
A TypeScript compiler API that strips types from a single file without performing full project-level semantic analysis — fast but limited diagnostics.
Downlevelling
Transforming modern JavaScript syntax into equivalent older syntax — async/await to generator state machines, optional chaining to ternary expressions.
Strict mode (tsconfig)
A bundle of flags including strictNullChecks, noImplicitAny, and strictFunctionTypes that catch common type bugs at compile time.
ESNext
A target alias meaning 'the latest ECMAScript proposals supported by this TypeScript version' — emits the most modern syntax with minimal downlevelling.
Type erasure
TypeScript types are removed at compile time and have no runtime representation — a TS file with types compiles to JS with the types stripped.
Diagnostics
Compiler-emitted errors, warnings, and suggestions about your source code, surfaced by TypeScript's checker even when transpilation succeeds.