The Document Object Model (DOM) is a fundamental concept in web development, representing the structure and organization of a web page's content. When a web page loads into a browser, the browser generates HTML to display the requested page, forming a tree-like structure known as the DOM. This structure allows for efficient manipulation and rendering of page content.

However, modifying the DOM (e.g., changing innerHTML) can lead to performance issues due to the need to parse and re-render the entire page. To address this, virtual DOMs were introduced, creating a copy of the real DOM stored in memory. When changes occur, a new virtual DOM is created, compared to the previous one, and the differences are applied to the real DOM.

This approach has become ubiquitous in modern web development libraries, leveraging algorithms like dif for efficient comparison. While virtual DOMs offer significant performance gains, considerations must be made for optimal performance.

Source: https://dev.to/sonaykara/why-virtual-dom-faster-rendering-and-performance-1cjh