In-Depth Understanding of React Source Code IV

This is the fourth part of our deep dive into the React source code. In this article, we will explore how React handles state changes and updates.

React Reconciliation Algorithm

React uses a reconciliation algorithm to determine which parts of the UI need to be updated when a component's state changes. The algorithm works by comparing the new virtual DOM with the previous one and calculating the minimum number of changes required to update the actual DOM.

The reconciliation algorithm has two phases:

1. Diffing: This phase compares the new virtual DOM with the previous one and generates a list of changes that need to be made to the actual DOM. This process is optimized using heuristics like "keys" and "memoization".

2. Reconciliation: This phase applies the list of changes generated in the diffing phase to the actual DOM. React uses a "commit" strategy to apply these changes in batches for better performance.

setState() and State Updates

When you call setState() in a React component, React schedules a state update by adding it to a queue. Each queued update goes through a validation process before it is applied to the component. If multiple updates are scheduled, React batches them together for performance reasons.

React also provides a callback function that gets called after the state has been updated. This allows you to perform additional tasks after the state has changed.

Here's an example of how setState() works:

----- ------- ------- --------------- -
  ------------------ -
    -------------
    ---------- - - ------ - --
  -

  ----------- - -- -- -
    --------------- ------ ---------------- - - -- -- -- -
      ------------------ -- --- ----------------------
    ---
  --

  -------- -
    ------ -
      -----
        --------- ----------------------
        ------- ---------------------------------------------
      ------
    --
  -
-

In this example, we have a counter component that increments its count state every time the button is clicked. The setState() function updates the count state and logs its new value to the console.

Conclusion

React's reconciliation algorithm and setState() function are essential parts of React's functionality. By understanding how they work, you can write more efficient and performant React applications. Remember to always optimize your code and use the right tools for the job.

来源：JavaScript中文网 ，转载请注明来源 本文地址：https://www.javascriptcn.com/post/5802