When you call setState in a React component, several things happen to manage the component's state and UI rendering effectively:
Asynchronous Update: setState actions are asynchronous. This means that setState does not immediately update the component's state but schedules an update. This behavior allows React to optimize performance by batching state updates that occur in close succession[3][4][5][7][8][9][10][14][15][16].
State Merging: When setState is called, the object passed to it is merged with the current state. This merging is shallow, which means that only the properties specified in the setState call are updated, while others remain intact[3][14][16].
Re-rendering: After state updates are processed, React re-renders the component to reflect the new state. This re-rendering happens at a convenient time after the state has been updated. React ensures that the DOM is updated efficiently by batching updates and reducing unnecessary renders[2][3][4][5][7][10][14].
Callback Function: setState can accept a callback function as its second argument. This function is executed after the state update has been applied and the component has re-rendered. This is useful for operations that need to occur after the state has been updated[1][3][5][6][7][8][9][15].
Handling Asynchronous Nature: Due to its asynchronous nature, accessing the state immediately after calling setState might not reflect the new values. Developers need to use the callback function or lifecycle methods like componentDidUpdate to work with the updated state[3][4][5][7][8][9][15].
Batching and Performance: React batches multiple setState calls into a single update cycle to optimize performance. This batching minimizes the number of re-renders and computational overhead involved in updating the DOM[3][4][7][8][9][14].
