React's Virtual DOM improves web application performance by providing a lightweight, in-memory representation of the user interface (UI) that only updates parts of the real DOM as needed, rather than re-rendering the entire DOM with every change. This technique enhances efficiency, reduces latency, and optimizes CPU and memory usage, especially in dynamic applications with frequent UI changes. The blog explains the differences between the Core DOM, Virtual DOM, and Shadow DOM, and outlines how to implement a Virtual DOM in JavaScript. It further details how React employs the Virtual DOM through a process called reconciliation, using algorithms to compare changes and update the real DOM efficiently. The blog also includes a deep dive into automated testing with Jasmine and Cloud Selenium Grid, showcasing how these tools can test web applications across multiple browsers and operating systems to ensure consistent performance and user experience.