ReactJS is a popular JavaScript library for building UI(user interfaces) components. When building a ReactJS web app, there are two primary ways to render the application: client-side rendering (CSR) and server-side rendering (SSR).
Client-side rendering (CSR) is a technique where the initial rendering of the application happens on the client-side, i.e., the browser. The server sends a minimal HTML document, which includes a reference to a JavaScript bundle. The browser downloads this JavaScript bundle and then executes it to render the application. In this approach, the user has to wait for the JavaScript bundle to be downloaded and executed before seeing any content. CSR is best suited for applications that are highly interactive and require frequent updates.
Server-side rendering (SSR) is a technique where the initial rendering of the application happens on the server. The server sends a fully rendered HTML document to the client, which the browser can display immediately. The client-side JavaScript code then takes over and re-renders the application as needed. In this approach, the user can see the content immediately, without waiting for the JavaScript bundle to be downloaded and executed. SSR is best suited for applications that require fast initial load times and good SEO.
In general, both CSR and SSR have their own advantages and disadvantages. CSR is good for highly interactive applications, whereas SSR is good for applications that require fast initial load times and good SEO. It's also possible to use a hybrid approach that combines both CSR and SSR to get the best of both worlds.