TypeScript Playground

This TypeScript Playground lets you test a snippet quickly without opening a full project. It runs the TypeScript compiler in your browser, shows type-checking diagnostics with line numbers, emits JavaScript, and can run simple output in a sandboxed console.

What This TypeScript Playground Does

The tool is designed for everyday TypeScript checks: validating union narrowing, testing generic helper types, comparing compiler targets, confirming strict-mode behavior, and reviewing the JavaScript that TypeScript emits. It is useful for learning, debugging a compact example, preparing an answer, or checking a small refactor before moving it into a project.

How to Use the TypeScript Compiler

1. Paste TypeScript into the editor or choose a quick example.
2. Select a JavaScript target and module format.
3. Enable strict mode and optional indexed access checking when you want tighter diagnostics.
4. Click Compile and Type Check, or leave auto compile enabled for live feedback.
5. Review diagnostics, inspect the emitted JavaScript, then run simple snippets in the sandboxed console.

Type Checking Notes

The browser compiler uses a compact built-in declaration file for common JavaScript objects such as arrays, strings, records, JSON, console, and timers. That keeps the playground fast and self-contained for snippets. If your code depends on React, Node.js, DOM APIs, or package-specific declarations, confirm the final result inside your project with its real tsconfig.json and installed type packages.

Examples and Use Cases

Use the playground when you want to isolate a type error from a larger codebase, compare how strict mode changes diagnostics, explain a TypeScript concept to a teammate, or check how a small snippet compiles to JavaScript. The built-in examples cover discriminated unions, generic record helpers, the satisfies operator, and intentional type mistakes so you can see both clean and failing compiler states.

• Validate a union type before adding it to an API response model.
• Test a generic helper without waiting for a full application build.
• Inspect emitted JavaScript when changing target or module options.
• Share a compact reproduction of a TypeScript diagnostic.

FAQ

Does this tool check TypeScript types?

Yes. It builds an in-browser TypeScript program and reports diagnostics from the compiler, including type errors, syntax errors, and compiler-option messages.

Can I change TypeScript compiler options?

Yes. The main controls cover JavaScript target, module output, strict mode, declaration emit, and noUncheckedIndexedAccess.

Why is a library type missing?

This playground intentionally uses a compact built-in type library. For framework, DOM, Node.js, or npm package types, use your local project setup.

Is the JavaScript runner safe?

The runner uses a sandboxed iframe for quick snippets. Avoid running untrusted code, and test real app code inside your normal development environment.