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Frameworks & web · #svelte
Learn how to add a global, SSR‑safe theme toggle to a Svelte app. Use a writable store, persist to localStorage on the client, and keep the UI reactive across all components.
Learn how to diagnose and fix common Svelte reactivity failures, specifically focusing on why array mutations and object updates often fail to trigger DOM changes.
When a Svelte component’s <code>$:</code> block runs too often, performance suffers. Derived stores offer memoized, source‑driven recomputation. This blog contrasts reactive statements and derived stores, shows a counter example, and gives a clear checklist for choosing the right tool.
Symptom After upgrading a project to Svelte 5, some components were migrated to runes ( $state , $derived , $effect ) while others still use legacy $: reactive statements. Everything compiles, but side effects appear to run earlier or later than before in components that sit at the boundary between the two styles — values update correctly, only the ordering
Async Triggered Reactive State Updates In a component that defines multiple reactive declarations using the $: label, an asynchronous operation (e.g., fetch, setTimeout) assigns a new value to a variable referenced by other reactive blocks. The compiler statically tracks dependencies, but the timing of the assignment may occur after the initial synchronous e
We are mid-migration from Svelte 4 to Svelte 5 and need to settle one configuration decision before it spreads across the codebase: how shared client state should be declared going forward. Today we have roughly a dozen Svelte stores (writable and derived) consumed with the $store auto-subscription syntax in components. Svelte 5 runes ( $state , $derived ) a
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