One of the most exciting features in React 19 is the React Compiler, which takes React to the next level. In previous versions, React would prepare the code to run in the browser during the bundling process. But now, the React Compiler compiles React code directly into HTML, CSS, and JavaScript, making applications much faster.

This kind of compiler already existed in Svelte, which is why Svelte has been significantly faster than React. With this new compiler, React 19 promises to boost performance much more.

Additionally, React often re-renders the UI unnecessarily when the state changes, which used to require manual optimization using memoization techniques like useMemo. React 19 will now handle these optimizations automatically, saving developers time and effort.