What are the key concepts in React 16+?

React 16 introduced a myriad of enhancements and new features that significantly improved both developer experience and app performance. Let’s delve into the key concepts of React 16 and its subsequent versions:

1. React Fiber: At the heart of React 16 is the introduction of Fiber, a new reconciliation engine. It brought about incremental rendering, enabling React to split rendering work into chunks and prioritize user interactions for a more responsive experience.

2. Fragments: React 16 introduced Fragments, allowing developers to return multiple child elements from a component’s render method without the need for an extra wrapping DOM element. This leads to cleaner DOM output and can help in improving performance.

3. Error Boundaries: Error handling became more robust with the advent of error boundaries. Components can now catch JavaScript errors anywhere in their child component tree, log those errors, and display a fallback UI.

4. Portals: Portals provide a way to render children into a DOM node outside of the parent DOM hierarchy, immensely helpful for UI patterns like modals and pop-ups.

5. Concurrent Mode (Experimental): Introduced in later versions post-16, Concurrent Mode is a set of features that help React apps remain responsive by rendering complex UIs smoothly and interruptibly. It’s a forward-looking enhancement, emphasizing non-blocking rendering.

6. Hooks: Although introduced in React 16.8, hooks represent a significant shift, allowing developers to use state and other React features in functional components, reducing the need for class components.

7. Strict Mode: React 16 introduced the `StrictMode` component, a tool for highlighting potential problems in an application, helping developers follow best practices and avoid the use of deprecated methods.

8. Suspense and Lazy Loading: Suspense allows components to “wait” for something before rendering, which, combined with React.lazy, facilitates code-splitting and dynamic imports, optimizing the loading of components.

React 16 and its subsequent updates have been instrumental in shaping the modern React ecosystem. They brought about essential improvements and tools that cater to both the performance and scalability needs of today’s web applications, ensuring React remains at the forefront of UI development.