module-tsx skill

module-tsx runs TypeScript and TSX directly in the browser — no build step, no bundler. It transpiles code on the fly and rewrites bare specifiers (like "react") to https://esm.sh/<pkg> automatically.

How to load it

<script type="module" src="https://esm.sh/module-tsx"></script>

Load this before any <script type="module-tsx"> tags.

Writing code

Use <script type="module-tsx"> like <script type="module"> but with full TypeScript and JSX support:

<script type="module-tsx">
  const greet = (name: string) => `Hello, ${name}!`
  console.log(greet("world"))
</script>

Or load an external file:

<script type="module-tsx" src="./main.tsx"></script>

React / TSX — zero config

Bare specifiers resolve to esm.sh automatically, so React just works with no import map needed. JSX without an explicit import React is fine too — it's auto-injected:

<div id="root"></div>
<script type="module-tsx">
  import { createRoot } from "react-dom/client";

  function App() {
    return <h1>Hello!</h1>;   // React auto-injected, no import needed
  }

  createRoot(document.getElementById("root")!).render(<App />)
</script>

Example complete page

<!doctype html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <title>My App</title>
    <script type="module" src="https://esm.sh/module-tsx"></script>
  </head>
  <body>
    <div id="root"></div>
    <script type="module-tsx">
      import { createRoot } from "react-dom/client";
      import "@tailwindcss/browser";

      interface Props { name: string }

      function Greeting({ name }: Props) {
        return <h1 class="text-2xl font-bold">Hello, {name}!</h1>;
      }

      createRoot(document.getElementById("root")!).render(<Greeting name="world" />);
    </script>
  </body>
</html>

Import maps — only when you need them

An import map is optional. Use one only when you need to:

• Pin a specific version (e.g. react@18 instead of latest)
• Deduplicate peer dependencies across packages

The import map must be declared before the module-tsx script tag, because module-tsx reads it at startup:

<script type="importmap">
  {
    "imports": {
      "react": "https://esm.sh/react@18",
      "react-dom/client": "https://esm.sh/react-dom@18/client"
    }
  }
</script>
<script type="module" src="https://esm.sh/module-tsx"></script>

Peer dependency deduplication

When a UI library (like @radix-ui/themes) depends on the same React as your app, both must resolve to the exact same URL or you get "Invalid hook call" crashes. Use ?deps= to tell the CDN which React to bundle against:

<script type="importmap">
  {
    "imports": {
      "react": "https://esm.sh/react@18",
      "react-dom": "https://esm.sh/react-dom@18",
      "react-dom/": "https://esm.sh/react-dom@18/",
      "@radix-ui/themes": "https://esm.sh/@radix-ui/themes?deps=react@18,react-dom@18",
      "@radix-ui/themes/": "https://esm.sh/@radix-ui/themes/"
    }
  }
</script>
<script type="module" src="https://esm.sh/module-tsx"></script>
<script type="module-tsx">
  import '@radix-ui/themes/styles.css' // .css files will be injected as <style> tags
</script>

Relative imports

.ts and .tsx files can be imported relatively — fetched and transpiled on the fly:

import { Button } from "./components/Button.tsx";

CSS imports

import "./style.css"; // injects a <style> tag into <head>
import styles from "./button.module.css"; // returns { root: "abc123_root", ... }

Dev vs Production

Use the dev build during development for a rich error overlay (runtime errors, failed imports, source-mapped stack traces with code frames):

<script type="module" src="https://esm.sh/module-tsx/dev"></script>

Use the production build for deployment (no error overlay, smaller footprint):

<script type="module" src="https://esm.sh/module-tsx"></script>

Common mistakes

• defer attribute: not supported. Use async or no attribute.
• Dual React: if a package depends on React as a peer, use ?deps=react@18 so it shares the same instance — otherwise you'll get hook errors.
• Import map ordering: if you use an import map, it must come before the module-tsx <script> tag.