When setState is called in a React component, it triggers a process that leads to potential updates in the component's output in the Document Object Model (DOM). Here's a detailed breakdown of how this process works:
1. Calling setState
When setState is invoked, it schedules an update to a component's state object. This method does not immediately update the component but rather enqueues changes to the component's state[14][17].
2. Asynchronous Update
setState is asynchronous, which means React may batch or defer the update until later. This batching optimizes performance by grouping multiple state updates into a single re-render for better performance[5][9][17].
3. Reconciliation Process
Once state updates are processed, React enters the reconciliation phase. During this phase, React compares the new state and props of the component with the previous state and props to determine if the component needs to be re-rendered[1][3][4][15][18].
Virtual DOM and Diffing Algorithm: React maintains a virtual DOM, which is a lightweight copy of the actual DOM. It uses this virtual representation to figure out the minimal changes required on the actual DOM. The diffing algorithm helps in identifying differences between the old and new virtual DOMs. It calculates the least number of operations needed to update the real DOM efficiently[3][4][18].
Component Tree Walkthrough: React walks through the component tree starting from the root. It compares each component's previous virtual DOM representation with the new one generated after state changes. If the component's type has changed, React will replace the entire subtree. If only properties (props) have changed, React will only update the attributes of the DOM elements[3][15][16].
4. Update the Real DOM
After determining the necessary updates during reconciliation, React batches these changes and updates the real DOM all at once. This approach minimizes the performance cost associated with DOM manipulations[3][15][18].
5. Lifecycle Methods and Hooks
During the update process, React calls various lifecycle methods (for class compone...
