What does the TypeScript Formatter and JavaScript Transpiler do?
Use this tool when you need a browser utility that formats TypeScript or erases type syntax and lowers supported language features into JavaScript for a selected target. It accepts one TypeScript file up to 2 MB and returns Prettier-formatted TypeScript or single-file JavaScript emitted by the TypeScript compiler. Results are deterministic for the same input except where cryptographic randomness, current time, or a live provider response is part of the task.
Transpilation is not project type checking or bundling
Use format mode for source maintenance. Use transpilation for a quick, isolated view of emitted JavaScript. Use the project compiler and bundler for authoritative type checking, dependency resolution, path aliases, declaration output, and production builds. This page never executes the pasted source or emitted result.
How do you use it?
- Choose Format TypeScript for readable source or Transpile to JavaScript to erase types and emit runnable syntax.
- For transpilation, select the intended ECMAScript target and choose ES module or CommonJS output.
- Paste one TypeScript file no larger than 2 MB, run the operation, then review and download the result.
Worked example
Erase TypeScript declarations from a typed function
Input
interface Tool { name: string; local: boolean }
const label = (tool: Tool): string => tool.local ? tool.name : `${tool.name} (API)`;Output
const label = (tool) => tool.local ? tool.name : `${tool.name} (API)`;Transpilation removes the interface and type annotations while preserving the program logic. The selected target controls whether newer JavaScript syntax is lowered.
Common errors and fixes
| Symptom | Likely cause | Fix |
|---|---|---|
| Code with an incorrect type still produces JavaScript. | The browser workflow uses isolated single-file transpilation, which reports syntax and compiler-option diagnostics but does not run whole-project semantic type checking. | Run tsc or the project build with its real tsconfig and dependencies before treating the code as type-safe. |
| An imported value is missing when the output runs. | Transpilation preserves or rewrites module syntax but does not resolve, download, or bundle imported dependencies. | Use the emitted file inside the project build or bundler that owns those dependencies. |
| The generated syntax or module wrapper is not accepted by the destination. | The selected ECMAScript target or module format does not match the browser, Node.js version, or package configuration. | Select a compatible target and choose ES module or CommonJS to match the destination runtime. |
Important behavior of TypeScript Formatter
Single-file transpilation does not resolve dependencies or perform semantic project type checking, and the emitted JavaScript still needs testing in its target runtime.
Standards and implementation references
- TypeScript Compiler API (opens in a new tab)Documents transpileModule as a single-source transpilation API and explains its isolated compilation boundary.
- TypeScript target option (opens in a new tab)Explains how the selected target controls JavaScript syntax lowering.
- Prettier browser documentation (opens in a new tab)Documents standalone browser formatting and explicit TypeScript and ESTree plugins.
Frequently asked questions about TypeScript Formatter
Does the TypeScript Formatter upload my input?
No. Processing runs in the current browser tab, and the page does not send tool input to a KitLumi processing endpoint.
What input does the TypeScript Formatter accept?
It accepts one TypeScript file up to 2 MB. The workspace checks the input and reports malformed or unsupported values before it produces a result.
What does the TypeScript Formatter produce?
It produces Prettier-formatted TypeScript or single-file JavaScript emitted by the TypeScript compiler. Copy and download controls appear when the output format supports them.
What limitation should I know?
Single-file transpilation does not resolve dependencies or perform semantic project type checking, and the emitted JavaScript still needs testing in its target runtime.
What changed?
Moved TypeScript transpilation to a Worker and added engine loading feedback, debounced input, and stale-result protection.