Fix MemoryError in Svelte in Production

Svelte/SvelteKit Memory Issues in Production

SvelteKit's server-side rendering can leak memory across requests if stores or module-level state aren't properly isolated. Client-side SPAs can also accumulate memory during long sessions.

Server-Side Store Leaks

Module-level writable stores in SvelteKit are shared across all requests on the server:

// BAD — shared between all users on the server
import { writable } from 'svelte/store';
export const userStore = writable(null);

// GOOD — use SvelteKit's locals or page data
// In +layout.server.ts
export async function load({ locals }) {
  return { user: locals.user };
}

Module-Level Caches

// BAD — grows with every SSR request
const cache = new Map();

export async function load({ params }) {
  if (!cache.has(params.id)) {
    cache.set(params.id, await fetchData(params.id));
  }
  return { data: cache.get(params.id) };
}

// GOOD — use bounded cache
import { LRUCache } from 'lru-cache';
const cache = new LRUCache({ max: 100, ttl: 60000 });

Client-Side Memory

Long-running SPAs accumulate memory from navigation:

<script>
  import { onMount, onDestroy } from 'svelte';
  import { browser } from '$app/environment';

  let interval;
  onMount(() => {
    interval = setInterval(fetchUpdates, 5000);
  });
  onDestroy(() => {
    clearInterval(interval);
  });
</script>

Always clean up timers, observers, and event listeners in onDestroy.

Bugsly captures both server-side errors (with request context) and client-side memory warnings from SvelteKit applications in a unified dashboard.