I am creating a simple chat app using react and node js. When using socket to establish a connection between server and client, I was wondering the point of using this package. Since react re-renders the page upon state change, I can fetch messages from my database and change the state, allowing for a presumably seamless chat application. Will there be any problems with such a chat application, where the chats would be displayed by fetching data from the database? Adding a new message would again update the database and the data would be fetched. So, the page would update with the new chat being displayed as it has been re-rendered due to change of state. So what is the need for socket in such an application ?
You could build what you describe without socket.io. Socket.io simply allows the messages to be delivered in real-time using websockets and a few other technologies so you don't have to build long-polling.
Said in a different way, when you fetch data from the database, you'll have react perform an API call and fetch new messages from a node.js API endpoint. This API call will need to be performed on a very short interval to make it feel like messages are showing up in real time.
This is one of many situations in programming where you could totally write something yourself, but there are industrial grade solutions that will help speed up your development.