In React, reconciliation is the process of comparing the virtual representation of a component's previous state with its new state, and determining the minimal set of changes needed to update the user interface efficiently. It's how React figures out what parts of the UI need to be updated when the state or props of a component change.
Here's a step-by-step explanation of the reconciliation process in React:
Virtual DOM: React uses a virtual representation of the DOM called the Virtual DOM. It's a lightweight copy of the actual DOM.
Render: When a component's state or props change, React re-renders the component and generates a new virtual representation of the component's UI.
Diffing: React takes the previous virtual representation (from the previous render) and the new virtual representation (from the current render) and performs a process called "diffing." Diffing involves comparing the two representations and identifying the differences between them.
Update Strategy: React employs an efficient update strategy based on the diffing process. It aims to minimize the number of actual changes made to the real DOM by only applying the necessary updates.
Reconciliation: Once React has identified the differences between the previous and new virtual representations, it performs the necessary updates to the real DOM to reflect the changes. This process is called reconciliation.
During reconciliation, React follows a few principles to optimize the update process:
- Elements of different types are considered different and are completely rebuilt from scratch.
- React tries to update the props of components if they have the same type.
- React uses a "key" prop on lists of elements to improve the efficiency of updates.
By following these principles, React ensures that the user interface remains in sync with the component's state and props while minimizing unnecessary DOM manipulations, resulting in better performance.
Reconciliation is a core concept in React, but you don't need to worry about it too much in your day-to-day development. React's reconciliation algorithm is highly optimized and handles most cases efficiently. However, understanding the basics of reconciliation can help you write more efficient and optimized React components when dealing with larger applications.