There is no rerender, when you call listen, then all scroll events will warn on chrome. See this entry from svelte: breaking the web

The original promise of React was that you could re-render your entire app on every single state change without worrying about performance. In practice, I don’t think that’s turned out to be accurate. If it was, there’d be no need for optimizations like shouldComponentUpdate (which is a way of telling React when it can safely skip a component)

A component shouldn’t break because it’s rendered more or less often.

useField() returns FieldRenderProps. It will manage the rerendering of any component you use it in, i.e. the component will only rerender if the field state subscribed to via useField() changes.

Since you often want to do calculations based on state, Svelte also has the “reactive declaration” symbol, $:. It’s like a let declaration, but whenever any variable referenced in the expression — count in this case — is updated, the expression is re-run, the new variable’s value is updated, and the component is re-rendered.

The heart of Svelte’s magic is “reactivity”. Every let declaration sets up a listener, where any time the variable is assigned to, the change triggers a render of the component. So when the increment function calls count++, the component will re-render, which will update the value shown to the user by Count: {count}.

To change component state and trigger a re-render, just assign to a locally declared variable.

Think of useRef as a useState that does not trigger a re-rendering of our component.

In the two years that I've been working with React professionally, I've never come to a point where I needed to force a re-render. I encourage you to read the article from the beginning if that's what you're here for because usually there's a better way of dealing with React components that aren't updating.