It's vanilla JS, doesn't bind you to specifc syntax and that's the main reason why I like svelte that it doesn't try to sandbox you into framework constraints.

When I'm prototyping components I like to manage the data where it appears, and not send it back and forth if there is no reason for it. I also don't like to be forced by a language to do things a certain way.

JavaScript is, of course, a dynamic language that allows you to add and remove objects and their members at any point in time. For many, this is precisely why they enjoy the language: there are very few constraints imposed by the language.