TypeScript Runner

What Is an Online TypeScript Runner?

TypeScript is a superset of JavaScript that adds a static type system. Browsers do not understand types, so every TypeScript project passes through a compiler that removes them and emits plain JavaScript. An online TypeScript runner performs that step in the browser and then executes the result, giving you a typed scratchpad with no local install.

Transpiling vs Type Checking

These are two different jobs, and knowing the difference explains what this tool can promise. Transpiling converts syntax: annotations are stripped, newer features are downlevelled if needed, and JavaScript comes out. Type checking analyses your whole program — every import, every declaration file — to prove that the types are consistent.

Fast tools such as esbuild, SWC and Babel transpile only, which is why modern build pipelines run type checking separately. This runner takes the same approach: it reports syntax diagnostics with line and column numbers, then runs your code. It does not claim to catch every type error, because doing that honestly would require loading the full standard library and any dependencies you reference.

What Works Here

• Interfaces and type aliases, including index signatures and mapped types.
• Generics with constraints, defaults and inference.
• Discriminated unions and exhaustive narrowing patterns.
• Classes with access modifiers, parameter properties, abstract members and static blocks.
• Enums, tuples, as const, satisfies, optional chaining, nullish coalescing.
• Async/await and top-level await, since output runs as a module.

How Execution Is Isolated

The emitted JavaScript is inserted into a document that runs inside a sandboxed iframe without allow-same-origin. That gives the frame an opaque origin, so the code cannot read this site's DOM, cookies or storage. Console messages and errors are forwarded to the panel over postMessage with source verification.

A Realistic Workflow

Use the runner for the part of TypeScript that benefits from immediate feedback: designing a type shape and confirming the runtime behaviour it wraps. Sketch the union, write the function that consumes it, log the results, and iterate. Once the shape is right, move it into your project where the full type checker, tests and lint rules apply. The playground shortens the exploratory phase without pretending to replace the compiler in CI.

Why It Loads the Compiler on Demand

The TypeScript compiler is a large download. Shipping it with every page view would slow the whole site for the majority of visitors who never open this tool. Instead it is fetched from a CDN the first time you press Run and then cached by your browser, which keeps page loads fast and subsequent runs instant.

Privacy

Your TypeScript source is transpiled and executed locally. Nothing is uploaded to Zubac Tools, and drafts live only in this browser's storage until you reset them.

Compare behaviour with the JavaScript Runner, build UI in the HTML, CSS & JavaScript Runner, or validate data shapes in the JSON Playground.

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