Why is HTML DOM slow?
Imagine a DOM which a list of 10 items on your web page and if because of any user interaction, web page just needs to update one of them, that’s not possible. In this case, the entire real DOM will be re-rendered. Just to update one item of the list of 10 items, entire list will be re-rendered.
Is the DOM slow?
What is slow, however, is the layout that browsers have to do whenever the DOM changes. Every time the DOM changes, browser need to recalculate the CSS, do layout, and repaint the web page. This is what takes time.