What is Reconciliation in React.js?
Reconciliation is the core React.js process that synchronises the virtual and real DOMs to enable its effective UI updates. It serves as the “engine” that drives React’s performance, attempting to prevent expensive complete page reloads by identifying only the updates that are required to the actual DOM. React starts this process by generating a new virtual DOM tree that reflects the most recent user interface whenever a component’s state or props are changed.
To determine exactly what has changed, a “diffing” mechanism is then used to compare this new virtual DOM to the old one. To further optimise efficiency, React batches these updates rather than applying them all at once. They can be executed during the lifecycle of an event or after a predetermined amount of time, as after a user interaction like typing or clicking a button. In the end, the user experience is improved and direct DOM manipulation is much reduced by applying only the minimal amount of operations necessary to change the actual DOM to its new state.
How Reconciliation Works
The process of reconciliation is initiated anytime the state or props of a component are altered. The following is a detailed explanation of what occurs:
New Virtual DOM Tree Creation: React creates a new Virtual DOM tree that reflects the modified UI elements and their properties whenever a component’s state or props change. This new tree is basically a new “blueprint” on the basis of the available data.
Diffing Algorithm: Comparing this newly created Virtual DOM tree with the prior Virtual DOM tree is then accomplished by React via an advanced “diffing” process. Due to its optimal linear time complexity (O(n)), this technique is very effective, even for big applications, in determining the differences between the two trees.
Calculation of Minimal Operations: The comparison is used by React to determine the bare minimum of operations needed to convert the old Virtual DOM which stands in for the current real HTML DOM into the new Virtual DOM. Avoiding needless updates is an important step that maximises performance.
Efficient Real DOM Update: Lastly, React only makes these specific, small adjustments to the HTML DOM. Saving a great deal of time, only the relevant DOM elements that require modification are updated rather than the full page being reloaded or rendered. This enables a seamless user experience and a quick response.
The so-called React Fibre reimplements the fundamental reconciliation mechanism, improving renderability and user interface responsiveness, especially in complicated settings.
The Importance of Keys
When working with lists of items or components, React uses unique properties known as keys to help with the reconciliation technique. Keys aid in Reacting:
Identify changes: By identifying which particular parts in the actual HTML Document Object Model (DOM) require alteration, React.js effectively updates the User Interface (UI) through the identification of changes. We refer to this essential process as reconciliation.
Maintain stable identity: React uses keys to monitor and reorganise array elements instead of re-rendering them when the list changes. Replace the array index with a unique item identifier to save time and avoid complications.
Code Example:
Look at a basic React functional component that shows a message and lets you edit it by clicking a button.
import React, { useState } from 'react';
const App = () => {
return (
<div className="flex flex-col items-center justify-center min-h-screen bg-gray-100 dark:bg-gray-900 text-gray-900 dark:text-white p-4">
<div className="bg-white dark:bg-gray-800 p-8 rounded-lg shadow-xl text-center">
<h1 className="text-2xl font-bold mb-4">State and Reconciliation Example</h1>
{/* Render the core component. */}
<MessageDisplay />
</div>
</div>
);
};
function MessageDisplay() {
const [message, setMessage] = useState("Hello, React!");
const handleChangeMessage = () => {
setMessage("Reconciliation in action!");
};
return (
<div className="flex flex-col items-center">
{/* This paragraph displays the current 'message' state.
When the state changes, this part of the UI will be updated. */}
<p className="text-lg mb-4">{message}</p>
{/* The button's onClick event is wired to the handleChangeMessage function. */}
<button
onClick={handleChangeMessage}
className="bg-blue-600 hover:bg-blue-700 text-white font-bold py-2 px-4 rounded-lg shadow-md transition duration-300 ease-in-out transform hover:scale-105"
>
Change Text
</button>
</div>
);
}
export default App;Output:
State and Reconciliation Example
Reconciliation in action!
Change TextExplanation of the Code Example
Initial Render: Rendering to the DOM is the first thing React does when MessageDisplay loads. <p>Hello, React!</p> and a button are also visible. This initial state is reflected in the real DOM once a virtual DOM tree is formed to represent it.
User Interaction (State Change): “Change Text” button clicks trigger the handleChangeMessage method, which calls setMessage(“Reconciliation in action!”). Thus, the message status is updated.
Reconciliation Triggered: State changes notify React to the need to refresh the user interface, starting reconciliation.
New Virtual DOM Tree: The New Virtual DOM Tree To obtain the most recent description of the user interface, React re-executes the MessageDisplay method. This time, “Reconciliation in action!” is the message. The same button and the message “Reconciliation in action!” are represented by a new Virtual DOM tree.
Diffing: Comparing this new Virtual DOM tree to the old one is done via React’s diffing method. The only difference, it astutely concludes, is the text included within the <p> tag. The button remains unchanged.
Minimal Real DOM Update: To prevent re-rendering the entire div or <p> element, React just updates the text node inside the <p> tag in the browser DOM. React’s speed and effectiveness are attributed to this focused improvement.
Conclusion
To sum up, React.js clever reconciliation mechanism ensures quick and effective UI updates by keeping the virtual and actual DOMs in sync with little work. React recognises only what has changed and updates only those portions of the real DOM by generating a new virtual DOM tree with each state or prop change and employing an optimised diffing method. This focused strategy enhances performance, prevents needless re-renders, and provides a seamless user experience.
This process is further improved by features like keys, which preserve consistent component IDs in lists, and React Fibre, which improves reconciliation to more responsively handle complex interfaces. In the end, reconciliation enables developers to concentrate on specifying the UI’s appearance, while React effectively decides how to update the DOM in the background.