Is it bad to not remove elements from HTML that aren't visible?

Question

I've made a slideshow using JQuery which at the moment just uses append() to add an <img> to a container that was previously defined. The slideshow automatically rotates through, returning back the the start after the final slide and continuing infinitely.

At the moment, I don't remove the previous image in the container at all. I haven't noticed anything change in terms of performance or my memory filling up - a behaviour that I'm used to in Flash if I were to continue adding elements without removing old ones.

Is it necessary to remove the old images, or are these never going to cause performance issues?

Answer 1

Some of this might be browser-dependent, but in general I would say that yes it is indeed "bad" not to clean up your old elements. Whether or not an element is visible, it is still adding a node to the structure of the DOM, and you cannot add to the DOM infinitely.

Unless perhaps the browser implements some sort of intelligent pruning algorithm that swaps out unused/non-visible portions of the DOM, but I've never heard of such a thing being done in practice.