React js is a library. But it is not a framework. React.js use for creating user interfaces. React is not a complete solution. Though now react is the most popular library to create user interfaces but we need to know to use other libraries.
DOM means “Document Object Model”. We use DOM API to change a document, style, and content. Now it is most popular because it created a common language between developers and browsers. React support all popular browsers including internet explorer 9 and above, although some polyfills are required for older browser such as IE 9 and IE 10.