Vite

Editing a component normally costs a full page reload. The Vite plugin gives component modules an accept boundary, so an edit replaces just that component’s subtree and leaves the rest of the page — scroll position, open panels, sibling state — exactly where it was.

import { defineConfig } from "vite";
import elementsKit from "elements-kit/integrations/vite";

export default defineConfig({
  plugins: [elementsKit()],
});

Using Astro? The Astro integration registers this for you — don’t add it twice.

Setup

The plugin needs the JSX transform pointed at elements-kit, which is the same tsconfig.json you already need for JSX:

{
  "compilerOptions": {
    "jsx": "react-jsx",
    "jsxImportSource": "elements-kit"
  }
}

That is the whole setup. The plugin is dev-only (apply: "serve") — production builds and SSR transforms emit nothing, so no HMR code ships.

What gets swapped

In dev the compiler imports elements-kit/jsx-dev-runtime, which renders every component through a signal holding its current implementation. An edit re-points that signal, one effect re-runs, and the old subtree is disposed and rebuilt.

The unit is the component, not the page or the mount root. Edit a child and its parent’s signals keep their values:

// Panel.tsx — editing this swaps Panel only
export function Panel({ rows }: Props<{ rows: string[] }>) {
  const open = signal(false);
  return <ul>{() => rows().map((r) => <Row label={r} />)}</ul>;
}

A swapped component re-runs, so its own state resets. Anything that must survive an edit goes in a module the edit doesn’t invalidate:

// transcript.ts — not re-evaluated when Panel.tsx changes
import { signal } from "elements-kit/signals";
export const turns = signal<Turn[]>([]);

Components the module doesn’t export — Row above — have no name to match against, so they rebuild when their parent does rather than on their own.

Mount through JSX

A component only gets a boundary if the JSX runtime rendered it. Calling it yourself bypasses the runtime entirely:

// before — no boundary, edits reload the page
document.getElementById("app")!.appendChild(new App().render());

// after — App swaps in place
render(document.getElementById("app")!, () => <App />);

What still reloads

Falling back to a reload is always correct, never silent staleness — a module that can’t be swapped calls import.meta.hot.invalidate() and Vite propagates normally.

Modules that render no JSX. The plugin keys off the runtime import the JSX transform adds, so a plain .ts module has nothing to mark it.
vite.config.ts and anything else outside the module graph.