The Interactive Guide to Rendering in React

What is rendering?Put simply, rendering is just a fancy way of saying that React calls your function component with the intent of eventually updating the View.When React renders a component, two things happen.

First, React creates a snapshot of your component which captures everything React needs to update the view at that particular moment in time. props, state, event handlers, and a description of the UI (based on those props and state) are all captured in this snapshot.

From there, React takes that description of the UI and uses it to update the View.

Source: The Interactive Guide to Rendering in React