React.js takes DOM to the next level by keeping in memory a virtual representation of a UI and synchronizing it with the real DOM. Means when the page is loaded, an empty container (HTML) is loaded first, and then React renders the page content into it. If some part of the page changes, only the data for this part of the page is reloaded (not the whole page), and the update and rendering of the necessary parts of the page are carried out on the client-side. It speeds up loading and rendering and makes the sites very responsive.
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