This is more of a feature request / discussion. Assume that you are rendering an infinitely scrollable table and are listening to changes using PubSub. When a PubSub message arrives, you want to update the element in the DOM, but only if is is actually currently rendered. If the element is not in the DOM, you do not want to insert it.

This can currently be achieved in some cases, e.g. when using pagination and there is a fixed page size. Then we can use at: -1, limit: rows_per_page which wants to append at the end, but limits the items to the number of items on the page. But even in this simple case this will fail if there is a page that is not already full. It also does not work in the example when using an infinite scrolled page that limits the maximum number of elements to, e.g., 3x the page size to have some buffer. On initial render, we render N items (limit is 3*N), therefore a stream_insert with limit 3*N would still append the element.

So I'd like to propose a function stream_update(stream, element) that can be used to update an element of a stream, if it is currently in the DOM that does not insert non-existing elements. What do you think?