Understanding the Commit Phase in React

In the world of React, understanding the various phases of its reconciliation process is crucial
for mastering its intricacies. One of these phases, the commit phase, plays a significant role
in updating the DOM and finalizing the changes made during the reconciliation process. In this
article, we'll delve into the commit phase in React and explore its significance through
illustrative examples.

What is the Commit Phase?

The commit phase in React occurs after the reconciliation phase, during which React updates the
virtual DOM and determines which changes need to be applied to the actual DOM. Once the
reconciliation process is complete, React enters the commit phase, where it applies the changes
to the DOM and performs any side effects, such as updating refs or firing lifecycle methods.

Example Scenario

Let's consider a simple example to illustrate the commit phase in action. Suppose we have a
React component that toggles the visibility of a div element when a button is clicked:

  

    
  
import React, { useState } from 'react';

  const ToggleComponent = () => {
    const [visible, setVisible] = useState(false);
  
    const toggleVisibility = () => {
      setVisible(!visible);
    };
  
    return (
      <div>
        <button onClick={toggleVisibility}>Toggle Visibility</button>
        {visible && <div>This div is now visible!</div>}
      </div>
    );
  };
  
  export default ToggleComponent;
  

In this example, when the button is clicked, the toggleVisibility function is
called, which toggles the value of the visible state. Depending on the value of
visible, the inner div is either rendered or removed from the DOM.

The Commit Phase in Action

During the commit phase, React applies the changes to the DOM that were determined during the
reconciliation phase. In our example, when the button is clicked and the
toggleVisibility function is called, React updates the DOM to reflect the new state
of the visible variable.

Side Effects and Lifecycle Methods

In addition to updating the DOM, the commit phase also performs any necessary side effects and
fires lifecycle methods. For example, if our component had a useEffect hook to perform some
action when the component mounts or updates, it would be executed during the commit phase.

import React, { useState, useEffect } from 'react';
  
  const ToggleComponent = () => {
    const [visible, setVisible] = useState(false);
  
    useEffect(() => {
      console.log('Component rendered or updated');
    });
  
    const toggleVisibility = () => {
      setVisible(!visible);
    };
  
    return (
      <div>
        <button onClick={toggleVisibility}>Toggle Visibility</button>
        {visible && <div>This div is now visible!</div>}
      </div>
    );
  };
  
  export default ToggleComponent;
  

In this example, the useEffect hook will execute its callback function during the
commit phase, logging "Component rendered or updated" to the console whenever the component is
rendered or updated.

Conclusion

The commit phase in React is a crucial step in the reconciliation process, where React applies
changes to the DOM and performs side effects. By understanding how the commit phase works and
its significance in the React lifecycle, developers can build more efficient and robust
applications with React.