React 19 Hooks vs Svelte 5 Runes: Benchmark & Architecture — Svelte 5 Guide

Both React 19 and Svelte 5 bring major architectural shifts. While React doubles down on compiler memoization (React Compiler) and server-first components, Svelte 5 transitions to signal-based compiler primitives (Runes).

State and Form Handlers

Comparing form handling and reactive state between React 19 useActionState and Svelte 5 $state:

Form & Action State

Managing async submission state.

❌ React 19

React 19 Implementation

typescript

import { useActionState } from 'react';
async function updateName(prevState, formData) {
  const name = formData.get("name");
  return await saveToDb(name);
}
export function Profile() {
  const [state, formAction, isPending] = useActionState(updateName, null);
  return (
    <form action={formAction}>
      <input name="name" disabled={isPending} />
      <button type="submit">Save</button>
    </form>
  );
}

✨ Svelte 5 (Runes)

Svelte 5 Runes

svelte

<script>
  import { enhance } from '$app/forms';
  let isPending = $state(false);
</script>
<form method="POST" use:enhance={() => {
  isPending = true;
  return async ({ update }) => {
    await update();
    isPending = false;
  };
}}>
  <input name="name" disabled={isPending} />
  <button type="submit">Save</button>
</form>

Rendering Architecture Comparison

Feature	React 19	Svelte 5
Reactivity Mechanism	Fiber Virtual DOM Tree Diffing	Signals (`$state`) with DOM Node Mutation
Component Model	Re-executes whole function on render	Executes setup once; updates DOM nodes directly
Bundle Impact	~45 kB runtime engine	~2-4 kB runtime engine
Re-render Optimization	Requires React Compiler / `useMemo`	Built-in granular dependency tracking

State and Form Handlers

Form & Action State

Rendering Architecture Comparison

The Batteries-Included Edge TS Framework