Svelte 5 Vs Svelte 4

1I'm using svelte 5 instead of svelte 4 here is an overview of the changes.
2# .cursorrunes for Svelte 5
3 
4## Overview of Changes
5 
6Svelte 5 introduces runes, a set of advanced primitives for controlling reactivity. The runes replace certain non-runes features and provide more explicit control over state and effects.
7 
8Snippets, along with render tags, help create reusable chunks of markup inside your components, reducing duplication and enhancing maintainability.
9 
10## Event Handlers in Svelte 5
11 
12In Svelte 5, event handlers are treated as standard HTML properties rather than Svelte-specific directives, simplifying their use and integrating them more closely with the rest of the properties in the component.
13 
14### Svelte 4 vs. Svelte 5:
15 
16**Before (Svelte 4):**
17```html
18<script>
19  let count = 0;
20  $: double = count * 2;
21  $: {
22    if (count > 10) alert('Too high!');
23  }
24</script>
25<button on:click={() => count++}> {count} / {double}</button>
26```
27 
28**After (Svelte 5):**
29```html
30<script>
31  import { $state, $effect, $derived } from 'svelte';
32  
33  // Define state with runes
34  let count = $state(0);
35  
36  // Option 1: Using $derived for computed values
37  let double = $derived(count * 2);
38  
39  // Reactive effects using runes
40  $effect(() => {
41    if (count > 10) alert('Too high!');
42  });
43</script>
44 
45<!-- Standard HTML event attributes instead of Svelte directives -->
46<button onclick={() => count++}>
47  {count} / {double}
48</button>
49 
50<!-- Alternatively, you can compute values inline -->
51<!-- <button onclick={() => count++}>
52  {count} / {count * 2}
53</button> -->
54```
55 
56## Key Differences:
57 
581. **Reactivity is Explicit**: 
59   - Svelte 5 uses `$state()` to explicitly mark reactive variables
60   - `$derived()` replaces `$:` for computed values 
61   - `$effect()` replaces `$: {}` blocks for side effects
62 
632. **Event Handling is Standardized**:
64   - Svelte 4: `on:click={handler}`
65   - Svelte 5: `onclick={handler}`
66 
673. **Import Runes**: 
68   - All runes must be imported from 'svelte': `import { $state, $effect, $derived, $props, $slots } from 'svelte';`
69 
704. **No More Event Modifiers**:
71   - Svelte 4: `on:click|preventDefault={handler}`
72   - Svelte 5: `onclick={e => { e.preventDefault(); handler(e); }}`
73 
74This creates clearer, more maintainable components compared to Svelte 4's previous syntax by making reactivity explicit and using standardized web platform features.
75