The key reason behind this feature is the component-based architecture of React. In React, everything is a component. A component is a modular, reusable piece of code that encapsulates specific functionality and renders a portion of a UI. This means that instead of writing an entire application from scratch, you can reuse components across different applications, allowing you to write less code and focus on building new features.

Another key feature of React is its declarative nature. When using React, you simply declare what you want to happen and let the framework handle the how. This allows developers to focus on the big picture of what they want their application to do, rather than getting bogged down in implementation details.

For example, if you want to render a list of items in a React component, you simply declare what that list should look like, and React will handle the details of rendering each item in the list. This declarative approach not only simplifies development but also makes the code more readable and easier to maintain.

One of the most significant benefits of this feature is that it allows developers to build applications that can run on different platforms, including the web, mobile, and desktop. React Native, a mobile development framework, uses the same declarative and component-based approach as React, allowing developers to build native applications for iOS and Android using a single codebase.

In conclusion, the “Learn once, write anywhere” feature of React has revolutionized the way we build web applications. This feature is made possible by React’s component-based architecture and declarative nature, which allow developers to write less code, reuse components across different applications, and focus on the big picture of what they want their application to do. React has changed the game for front-end development, and its impact will be felt for years to come.