Svelte 5: A Different Kind of Framework

While React 19 and Vue 4 continue to refine their virtual DOM approaches, Svelte has taken a completely different path. Svelte 5 — released in late 2025 — introduces Runes, a fine-grained reactivity system that compiles away entirely, leaving zero framework overhead at runtime.

This isn’t just an incremental update. Runes represent a fundamental rethinking of how reactivity works in web applications.

Photo by Ilya Pavlov on Unsplash

What Are Runes?

Runes are compiler-aware JavaScript primitives prefixed with $. Unlike React hooks (which are runtime function calls) or Vue’s ref() (which wraps values in reactive objects), Runes are compile-time signals — the Svelte compiler transforms them into highly optimized vanilla JavaScript.

<script>
  // OLD Svelte 4 — reactive via assignments
  let count = 0;
  $: doubled = count * 2;

  // NEW Svelte 5 — explicit Runes
  let count = $state(0);
  let doubled = $derived(count * 2);
</script>

<button onclick={() => count++}>
  Count: {count}, Doubled: {doubled}
</button>

The key difference: Runes work anywhere in JavaScript, not just in .svelte files.

The Five Core Runes

1. $state — Reactive State

// works in plain .js/.ts files too!
export function createCounter(initial = 0) {
  let count = $state(initial);
  
  return {
    get value() { return count; },
    increment() { count++; },
    reset() { count = initial; },
  };
}

For deep reactivity on objects:

<script>
  let user = $state({
    name: "Alice",
    address: { city: "Seoul" }
  });
  
  // This triggers reactivity — Svelte 5 tracks deep mutations
  user.address.city = "Busan";
</script>

2. $derived — Computed Values

<script>
  let items = $state([1, 2, 3, 4, 5]);
  
  // Only re-computes when items changes
  let total = $derived(items.reduce((sum, n) => sum + n, 0));
  let average = $derived(total / items.length);
  
  // Derived with complex logic
  let stats = $derived.by(() => {
    const sorted = [...items].sort((a, b) => a - b);
    return {
      min: sorted[0],
      max: sorted[sorted.length - 1],
      median: sorted[Math.floor(sorted.length / 2)],
    };
  });
</script>

<p>Total: {total}, Average: {average.toFixed(2)}</p>
<p>Min: {stats.min}, Max: {stats.max}, Median: {stats.median}</p>

3. $effect — Side Effects

<script>
  let query = $state("");
  let results = $state([]);
  let loading = $state(false);
  
  $effect(() => {
    if (!query.trim()) {
      results = [];
      return;
    }
    
    loading = true;
    const controller = new AbortController();
    
    fetch(`/api/search?q=${query}`, { signal: controller.signal })
      .then(r => r.json())
      .then(data => {
        results = data;
        loading = false;
      })
      .catch(() => {});
    
    // Cleanup runs before re-execution or on destroy
    return () => controller.abort();
  });
</script>

4. $props — Component Props

<script>
  // Explicit, type-safe props with defaults
  let {
    title,
    count = 0,
    onUpdate = () => {},
    ...rest  // spread remaining props
  } = $props();
</script>

<div {...rest}>
  <h2>{title}</h2>
  <button onclick={() => onUpdate(count + 1)}>
    Count: {count}
  </button>
</div>

5. $bindable — Two-Way Binding

<!-- Child.svelte -->
<script>
  let { value = $bindable() } = $props();
</script>
<input bind:value />

<!-- Parent.svelte -->
<script>
  let name = $state("Alice");
</script>
<Child bind:value={name} />
<p>Hello, {name}!</p>

Real-World Performance: Svelte 5 vs React 19 vs Vue 4

Benchmark results from our production e-commerce dashboard (1,000 product cards, real-time price updates):

Svelte 5’s compile-time approach eliminates the virtual DOM diffing overhead entirely.

Building a Real Component: Data Table with Sorting & Filtering

<!-- DataTable.svelte -->
<script>
  let {
    data = [],
    columns = [],
    pageSize = 20,
  } = $props();

  let searchQuery = $state("");
  let sortKey = $state(null);
  let sortDir = $state("asc");
  let currentPage = $state(1);

  let filtered = $derived.by(() => {
    if (!searchQuery.trim()) return data;
    const q = searchQuery.toLowerCase();
    return data.filter(row =>
      columns.some(col => String(row[col.key]).toLowerCase().includes(q))
    );
  });

  let sorted = $derived.by(() => {
    if (!sortKey) return filtered;
    return [...filtered].sort((a, b) => {
      const va = a[sortKey];
      const vb = b[sortKey];
      const dir = sortDir === "asc" ? 1 : -1;
      return va < vb ? -dir : va > vb ? dir : 0;
    });
  });

  let totalPages = $derived(Math.ceil(sorted.length / pageSize));
  
  let paginated = $derived(
    sorted.slice((currentPage - 1) * pageSize, currentPage * pageSize)
  );

  function toggleSort(key) {
    if (sortKey === key) {
      sortDir = sortDir === "asc" ? "desc" : "asc";
    } else {
      sortKey = key;
      sortDir = "asc";
    }
    currentPage = 1;
  }
</script>

<div class="table-container">
  <input
    type="search"
    bind:value={searchQuery}
    placeholder="Search..."
    oninput={() => currentPage = 1}
  />

  <table>
    <thead>
      <tr>
        {#each columns as col}
          <th onclick={() => toggleSort(col.key)} class:active={sortKey === col.key}>
            {col.label}
            {#if sortKey === col.key}
              {sortDir === "asc" ? " ↑" : " ↓"}
            {/if}
          </th>
        {/each}
      </tr>
    </thead>
    <tbody>
      {#each paginated as row (row.id)}
        <tr>
          {#each columns as col}
            <td>{row[col.key]}</td>
          {/each}
        </tr>
      {/each}
    </tbody>
  </table>

  <div class="pagination">
    <button disabled={currentPage === 1} onclick={() => currentPage--}>Prev</button>
    <span>{currentPage} / {totalPages}</span>
    <button disabled={currentPage === totalPages} onclick={() => currentPage++}>Next</button>
  </div>
</div>

This is 122 lines of clean, readable code. The equivalent React component with useMemo, useCallback, and useState would be 200+ lines.

SvelteKit 2 + Svelte 5: Full-Stack in 2026

SvelteKit 2 integrates seamlessly with Svelte 5 Runes:

// +page.server.ts
export async function load({ params, fetch }) {
  const product = await fetch(`/api/products/${params.id}`).then(r => r.json());
  return { product };
}

export const actions = {
  addToCart: async ({ request, locals }) => {
    const data = await request.formData();
    await locals.db.cart.add(locals.userId, data.get("productId"));
    return { success: true };
  },
};

<!-- +page.svelte -->
<script>
  import { enhance } from "$app/forms";
  
  let { data } = $props();
  let { product } = data;
  
  let quantity = $state(1);
  let adding = $state(false);
</script>

<h1>{product.name}</h1>
<p>${product.price}</p>

<form method="POST" action="?/addToCart" use:enhance={() => {
  adding = true;
  return async ({ update }) => {
    await update();
    adding = false;
  };
}}>
  <input type="hidden" name="productId" value={product.id} />
  <input type="number" bind:value={quantity} min="1" max="99" />
  <button disabled={adding}>
    {adding ? "Adding..." : "Add to Cart"}
  </button>
</form>

Migration from Svelte 4

Svelte 5 ships with a migration tool:

npx sv migrate svelte-5

Key changes to watch for:

Should You Switch to Svelte 5?

Yes, if:

• Performance and bundle size are priorities
• You’re starting a new project
• Your team values simplicity over ecosystem size

Consider carefully if:

• You’re deep in the React ecosystem (libraries, tooling, team knowledge)
• You need React Native / cross-platform
• Enterprise requirements demand the largest talent pool

The Svelte 5 reactivity model is genuinely superior to hook-based approaches for most use cases. The smaller ecosystem is the only meaningful trade-off in 2026.

Photo by Ilya Pavlov on Unsplash

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