> Svelte gives you an elegant way to use CSS in your components with <style> tags, why not implement transitions and animations in CSS there?
Because CSS has no hooks into HTML lifecycle. If you want to nimate something that appears in the DOM, or disappears from the DOM elegantly, CSS ain't it.
That's why almost every single framework outside Svelte struggles with animations and employs increasingly bizarre and brittle workarounds to make them work.
Vue handles it just fine with doing the hard work behind the scenes and just passing you some CSS classes to connect your animations to (and there are JS events to use as well if you need a JS animation). Main difference is Svelte gets the benefit of being able to do some fancier stuff like items changing order or doing more than just entering/exiting. Vue has this as well, but not as easy to use.
That being said I overall prefer the Vue CSS approach to animation, it inspired my brother and I to make https://animxyz.com which has been my most successful side project yet. We wanted to make it work for Svelte as well but they don't have the CSS classes so we can't hook into their events the same.
Because CSS has no hooks into HTML lifecycle. If you want to nimate something that appears in the DOM, or disappears from the DOM elegantly, CSS ain't it.
That's why almost every single framework outside Svelte struggles with animations and employs increasingly bizarre and brittle workarounds to make them work.