React and Vue create a parallel “virtual DOM” that tracks all of the moving parts and only at the last microsecond do they hand off a clean, optimized collection of tags to the browser to render.

The concept of a virtual Document Object Model (DOM) was first introduced by the JavaScript framework React in 2013 and is still used today, both by React and other frameworks like Vue.js.

One such approach used by Vue.js is called "tree flattening," in which the framework splits the virtual DOM tree into several blocks, each containing a potentially large set of nodes.