If one has to answer what is react js then, React is a Javascript library that one attaches to any existing stack and makes UI dynamic. React was developed by Facebook in 2011 for Facebook only, and they made the code public by 2013. Before reacting to Js we had a primitive concept of DOM, but with react we have virtual DOM. Its an interesting concept about which in detail we will discuss just below but for starters, DOM which is a Document object model where when a browser loads a webpage it converts all the elements as an object with the root as a document. Now, when you add or modify a data on a web page, besides its simple when you click load more nodes get attached to the tree, but if you alter some data you need to refresh it again. Earlier on Facebook, they used to update notification with +1 so that when you click on it a webpage gets reloaded and so does data. Now, with virtual DOM where you get to modify the node in real-time as all the elements now get to are treated as attachable separate components whose value of nodes change with the script. These are too many terminologies, lets talk about them one by one.