Declarative Style: A declarative style, like what react has, allows you to control flow and state in your application by saying "It should look like this". An imperative style turns that around and allows you to control your application by saying "This is what you should do".
Virtual DOM : The virtual DOM (VDOM) is a programming concept where an ideal, or “virtual”, representation of a UI is kept in memory and synced with the “real” DOM by a library such as ReactDOM. This process is called reconciliation.
Community Support : React has a large base of developers and supporters. Since it is a old library you can find most of the answer in the Community.
SEO: React on its own is not SEO friendly and everything works on Virtual DOM it is difficult of web crawler to find the content but if you are using Nextjs or Gatsby you can optimize you site for SEO.
SPA : One of the main Advantage of React is that We can create Single page Applications ie our site will not reload when change the page. UI is changed without Refresh.
Github repo of React is: