People generally mean their manipulation of DOM is effectively slow. That's a perfectly accurate statement, but the problem is calling the DOM slow as a result.

People generally mean their manipulation of DOM is effectively slow. That's a perfectly accurate statement, but the problem is calling the DOM slow as a result. The real culprit is often that doing stupid things with the DOM cause style recalcs, reflows, layouts, compositing, painting, etc. Those are all comparatively expensive.