React and the Virtual DOM

As a software engineering student, learning to manipulate the Document Object Model (DOM) is an important JavaScript skill. Most software engineers learn React after they have learned JavaScript. React is known for being incredibly powerful when it comes to creating responsive user interfaces. One main feature that sets React apart from other JavaScript frameworks is its virtual DOM. In this article, I will outline the React virtual DOM, including how it functions and differs from the browser-based DOM.

Before I discuss the virtual DOM, though, here's an example of how React removes DOM manipulation from the user and handles it on its own. Take the following code snippet example of an array of dog objects, and code written in JavaScript to take the objects and place them in part of a table:

dogList.forEach((dog, index) => {
    let dogRow = document.createElement('tr');
    let dogName = document.createElement('td');
    dogName.innerText = dog.name;
    dogRow.appendChild(dogName);
    let dogBreed = document.createElement('td');
    dogBreed.innerText = dog.breed;
    dogRow.appendChild(dogBreed);
    let dogSex = document.createElement('td');
    dogSex.innerText = dog.sex;
    dogRow.appendChild(dogSex);
    let dogEdit = document.createElement('td');
    let dogEditBtn = document.createElement('button');
    dogEditBtn.id = `${dog.name}-${index+1}`;
    dogEditBtn.innerText = 'Edit';
    dogEditBtn.addEventListener('click', event => editDog(event));
    dogEdit.appendChild(dogEditBtn);
    dogRow.appendChild(dogEdit); 
    dogData.appendChild(dogRow);
})

Here's the same example in React:

dogList.map( (dog, index) => {
    return (
        <tr>
            <td>{dog.name}</td>
            <td>{dog.breed}</td>
            <td>{dog.sex}</td>
            <td>
                <button 
                    id={`${dog.name}-${index+1}`} 
                    onClick={editDog}>
                    Edit
                </button>
            </td>
        </tr>
    )
});

Much simpler, right? Thanks to React handling any DOM manipulation plus having the virtual DOM to track and update changes makes coding much easier.

What exactly is the Virtual DOM?

The virtual DOM serves as a virtual representation of the real Document Object Model (DOM) within a React application. It acts as a layer between your application's data and the actual DOM itself. In React, you no longer manipulate the DOM directly, though technically you could; however, not recommended. The virtual DOM was introduced to improve performance and enhance user experience by reducing updates to the real DOM.

How does the Virtual DOM operate?

Here is a breakdown of the virtual DOM as it occurs in the application:

When you first load a React application or component, it creates a virtual replica of the DOM. This virtual representation, often referred to as the DOM tree, reflects the structure of the DOM. When an event triggers a change in the application's state, like user interaction or data fetching, React re-renders the component.

The virtual DOM tree represents the state of the component that was just changed or updated. Next, React compares the virtual DOM tree with the previous one using a process called "diffing." This involves analyzing the differences between the two trees to determine what has changed. Once these differences are identified, React calculates an update to parts of the real DOM that changed. This ensures that a minimal amount of updates are applied to reflect the state of the application's UI.

Finally, React applies these updates to the standard DOM so that it accurately reflects and displays the updated state (version) of your application.

The virtual DOM has some advantages in React over the standard DOM. These are:

1. Improved Performance:
   Traditional DOM manipulation can be sluggish and inefficient particularly when dealing with user interfaces. The virtual DOM minimizes the number of updates made to the DOM resulting in performance enhancements. React's "diffing" algorithm ensures that only the necessary parts of the DOM are modified. This reduces rendering times and enhances user experience.

2. Cross Browser Compatibility:
   Dealing with browser compatibility issues can be quite challenging for many developers. React simplifies this by providing its own representation of the DOM. This enables developers to write code that behaves across browsers without requiring extensive browser-specific workarounds.

3. Simplified Debugging:
   The virtual DOM streamlines the process of testing and debugging React applications. Since the virtual representation of the DOM is essentially JavaScript objects, it becomes much easier to inspect and manipulate during development. This helps with identifying any issues within your code.

4. Enhanced Workflow for Development:
   The DOM offers developers the advantage of focusing on writing code that describes the desired UI state rather than getting caught up in the intricate details of manipulating the DOM. For me, this is the biggest advantage of React. In JavaScript, developers learn to write code that specifically describes what needs to happen. That includes querying the DOM to identify, find, and directly manipulate developments. With React, developers describe what the code will do instead of how to do it. This abstraction results in manageable code and a more enjoyable development experience.

Conclusion

In React development, the virtual DOM serves as a tool that improves performance, simplifies coding, and ensures consistency across browsers. By understanding its functionality and how it differs from the DOM, JavaScript, and React, developers can utilize its potential to create more efficient and easily maintainable user interfaces. Working with React and having the virtual DOM isn't just a recommended approach; it's an aspect of unleashing React's full capabilities and making the web development process less tedious and more satisfying.