What does React.js primarily focus on?Back-end developmentMobile app developmentFront-end developmentDatabase managementPrevious

React.js primarily focuses on Front-end development.

Explanation:

React.js is a JavaScript library developed by Facebook for building user interfaces, especially for single-page applications where dynamic content is displayed. Its primary emphasis is on the front-end development aspect, enabling developers to create reusable UI components that manage their own state. This allows for a more responsive and interactive user experience.

React employs a virtual DOM to optimize rendering performance, making it efficient for updating and rendering just the components that change, rather than reloading the entire page. This feature is crucial for high-performance web applications. In contrast, back-end development relates to server-side logic, database interactions, and application programming interfaces (APIs), which are outside the core focus of React.