React UI

For any val that renders a UI, prefer to build it with React components in .tsx files, unless the user states otherwise. The templates/react-hono-starter template is set up for this — start there with remix_val instead of building from scratch.

File conventions

Put markup, styles, and scripts in real files — avoid template literal strings (e.g. new Response(\...`)`). Code in template strings has no syntax highlighting, no linting, no type checking, and is unreviewable.

• .tsx — React/JSX components, any UI with logic or interactivity
• .html — purely static markup
• .ts — server code and scripts

Build UI component by component in .tsx files. Compose small components rather than rendering one giant page.

Styling: Twind + Tailwind

Prefer Twind to apply Tailwind utility classes at runtime — no build step required. Add the script to your HTML shell:

<script src="https://cdn.twind.style" crossorigin></script>

Then use Tailwind classes directly in JSX:

<div className="flex items-center gap-4 p-6 rounded-lg bg-white shadow">
  <h1 className="text-2xl font-bold">Hello</h1>
</div>

Avoid inline <style> tags, CSS-in-JS objects, or separate .css files, unless the user says otherwise.

Serving assets: versioned + immutable

Serve client modules with serveImmutableFile from std/utils — browsers cache them immutably, and publishing bumps the val's version, which invalidates automatically (full pattern: the client-side-js skill). A never-cached frontend/root.tsx shell (hono/jsx) stamps the entry and favicon with immutableFileUrl:

// frontend/root.tsx — in the Root() HTML shell:
<script src={immutableFileUrl("/frontend/index.tsx")} type="module" />

// index.ts:
app.get("/", (c) => c.html(Root()));
app.get("/__immutable/*", (c) => serveImmutableFile(c.req.path));

View source link

Every UI val should expose a way for users to see and remix its source. Both parts are required:

1. Backend route:

   import { parseVal } from "https://esm.town/v/std/utils/index.ts";
   app.get("/source", (c) => c.redirect(parseVal().links.self.val));
   

2. Visible link in the frontend:

   <a href="/source">view source</a>
   

React version pinning

A common error — "Cannot read properties of null (reading 'useState')" — means a React sub-dependency is loading a different React version. Pin all React-related imports to 18.2.0:

import SomeLib from "https://esm.sh/some-lib?deps=react@18.2.0,react-dom@18.2.0";

Assets

Do not use external images or hosted assets that may break. Prefer:

• Emojis or unicode symbols
• Inline SVG
• Icon fonts via CDN (Lucide, Font Awesome)

Surfacing client-side errors

To send browser errors back to val logs (visible via get_logs), include this script in your HTML shell:

<script src="https://esm.town/v/std/catch"></script>

Verifying changes

After editing a UI val, call fetch_val_endpoint to confirm the page renders without error, then check get_logs for any client-side errors. Don't report the change as done without both.