React Native Templates for iOS and Android

React Native is used for building mobile applications. It allows developers to use React along with native platform capabilities to build apps for iOS and Android. With React Native, developers can write in JavaScript while still delivering a real native user interface, allowing for shared codebases between platforms to reduce development time and cost.

React and React Native are both open-source projects from Facebook that deal with user interfaces, but they are used for different purposes.

1) React (also known as React.js) is a JavaScript library used for developing web interfaces. It allows developers to create reusable UI components and manage them in a virtual DOM.

2) React Native is a framework for building mobile applications using JavaScript and React. It provides a platform to develop mobile applications that can run on Android, iOS, and other platforms. With React Native, developers can use native components in combination with React. In simple terms, React is for web development, while React Native is for mobile app development.

No, WhatsApp is not built on React Native. WhatsApp is primarily built on Erlang programming language. However, for WhatsApp Web, it is built using ReactJS JavaScript library, which is also developed by Facebook.

React Native is a framework that allows developers to create mobile applications using Javascript and React, a JavaScript library for building user interfaces. If you are already familiar with JavaScript and React, which are both popular tools in web development, then learning React Native would be relatively easier. However, if you do not have any experience with these tools, there might be a steep learning curve initially as you also have to deal with mobile-specific challenges and understanding basic concepts of React. This could make learning React Native a bit challenging but with proper resources and dedication, you can grasp it efficiently. It's important to note that while learning React Native alone can allow you to make simple apps, becoming proficient often requires a well-rounded understanding of other technologies like JavaScript ES6, Redux, JSX, APIs, Mobile CLI, etc for a more professional app development.

Yes, Netflix still uses React for certain parts of its user interface, particularly on their Gibbon platform which is used for low performance TV devices. However, it's important to note that Netflix, like many large web applications, utilizes a mix of various technologies, frameworks, and systems in order to meet their wide range of needs and capabilities.

React Native is not being replaced; it remains a widely used option for cross-platform mobile application development. However, other options like Flutter (from Google) and Swift UI (from Apple) are also gaining popularity and providing competition in the market. The choice largely depends on the specific requirements and circumstances of a project, rather than one universally 'replacing' another.

There might be several reasons why someone chooses not to use React Native for their project:

1. Performance: Even though React Native's performance is pretty good, it can't really match up to what you can achieve with native languages. Apps with heavy animations or complex user interactions may run more smoothly if built in Swift or Kotlin, for example.

2. Limited API Access: React Native doesn't fully support all of the APIs or functionality that's offered by the native platforms, which may limit what a app can do.

3. Complex UI: Creating complex user interfaces might be easier and look a lot better using native development tools.

4. Learning Curve: React Native's learning curve can be quite steep, particularly if you are new to JavaScript.

5. Package Dependency: React Native relies on third-party libraries which may present a risk considering stability and compatibility issues.

6. Debugging: Debugging can oftentimes be more difficult than debugging a native application, as errors can sometimes be cryptic and hard to track down.

7. Still Evolving: React Native is still relatively new and evolving which can cause a lack of continuity if breaking changes are introduced in updates. All these factors may result in a longer development iteration compared to using a fully native solution, especially for complex projects.