Reconciliation is what happens when a React element is rendered. It first computes the virtual DOM tree that will render the element's current state and props. Then, this tree is compared to the existing tree for the element, assuming it has been rendered at least once already. The reason that React does this is because reconciling changes like this in JavaScript, before interacting with the DOM, is more performant. DOM interactions are relatively expensive compared to simple JavaScript code. Additionally, there are a number of common cases that the React reconciler has heuristics for.
React handles all of this for you—you just need to think about writing declarative React components. This doesn't mean that you'll ...
