Are there differences in rendering between React versions (e.g., 17th and 19th)? What do you know about concurrent rendering and Fiber?

There may be changes between React 17 and React 19 (if we talk about future versions), but a key major change in React was the architecture Fiber, introduced in React 16.

Fiber is a new internal rendering architecture that allows React to break work into small chunks and perform it asynchronously, pausing and resuming the rendering process. This enables the implementation of concurrent rendering.

Concurrent rendering is an approach where React can pause less important updates and switch to more important ones, improving interface responsiveness. For example, user input will not be blocked by long rendering.

In React 17, concurrent rendering was not fully available by default, but in newer versions (React 18 and beyond), it has become part of new APIs such as createRoot and startTransition.

Thus:

• React 17 is classic rendering with Fiber, but without full concurrent mode.
• React 18+ supports concurrent rendering with new APIs.

Fiber is the foundation that enabled these improvements, making rendering more flexible and responsive.