Best practices for efficient and smooth DOM operations

Anton Ioffe - November 6th 2023 - 8 minutes read

The power, performance, and fluidity of your web applications can be significantly influenced by your approach to JavaScript and the Document Object Model (DOM). However, efficient DOM manipulation isn't always an easy task and requires an understanding of many considerations such as reducing access, optimizing updates, and delegating events, not to mention the ability to identify and resolve performance bottlenecks. In this article, we will delve into these critical aspects, demystifying how they enhance the user experience and impact your application's overall performance. Through a series of practical tips, insightful concepts, and real-world code examples, you'll gain an exclusive toolkit of best practices for making your DOM operations as smooth and efficient as possible.

The basics of efficient DOM manipulation

DOM manipulation is the essence of dynamic and interactive web applications. Simply put, it involves modifying the structure, style, or content of the DOM (Document Object Model) using JavaScript. The DOM is a hierarchical representation of an HTML document, comprising of nodes corresponding to elements on a webpage. Efficient DOM manipulation means that changes to the DOM are precise, minimal, and carefully managed – a pre-requisite for smooth and responsive web applications.

Delving further, efficiency in DOM manipulation primarily deals with how effectively you select, modify, and navigate through these DOM nodes. For instance, you should be able to robustly select elements using JavaScript, from basic selection methods to more advanced queries. Mastery over this aspect is crucial as it forms the basis for subsequent manipulations.

Moreover, efficient DOM manipulation necessitates the dynamic alteration of content within selected elements. It's about creating fluid web pages which change and adapt in real-time. This could involve changing attributes such as class names and styles, or the content of the webpage itself. Ultimately, these modifications should enhance the visual appeal and functionality of your webpage, without creating any performance bottlenecks.

Lastly, traversing (navigating through parent and child nodes) the DOM is a vital skill in effective DOM manipulation. Understanding the tree-like structure of the DOM and knowing how to correctly reference different nodes helps in shaping a robust and efficient DOM manipulation strategy. Remember, the more you engage with the DOM, the more you'll uncover its nuances and harness its full potential. So, practice and experiment with these basic principles and watch your web applications become more responsive and interactive.

Reducing and optimizing DOM access

The efficiency of your JavaScript operations can depend significantly on how frequently your code interacts with the Document Object Model (DOM). By reducing DOM access, you can optimize your code's performance and make the user interface (UI) appear faster and more responsive to users. This involves minimizing the number of DOM lookups, which can be one of the most intensive operations your JavaScript performs. Be sure to limit your interactions with the DOM, and where possible, store references to DOM nodes for repeated access.

One way of implementing this is by caching frequently accessed elements. Instead of traversing the DOM each time you need to use an element, you can store a reference to it in a variable for faster access. Consider the following code, which improves performance by caching the result of a DOM query in a local variable, thus reducing further DOM interactions:

// Without caching
for (let i = 0; i < document.getElementsByTagName('p').length; i++) {
    document.getElementsByTagName('p')[i].style.color = 'blue'; // Repeated DOM access

// With caching 
const paragraphs = document.getElementsByTagName('p');
for (let i = 0; i < paragraphs.length; i++) {
    paragraphs[i].style.color = 'blue'; // Access cached DOM nodes

In the second code block, the 'getElementsByTagName' method only interacts with the DOM once, drastically improving the operation's speed on large documents. Remember, it's not unusual for modern web pages to have thousands of elements, making every DOM interaction count.

In addition to caching, using local variables to reference DOM nodes also helps optimize your code's performance. Instead of repeatedly accessing the same DOM node through document.getElementById or similar methods, refer to the node using a local variable:

// Without local variable
document.getElementById('myElement').style.display = 'none'; // DOM access
document.getElementById('myElement').textContent = 'Hello, World!'; // Repeated DOM access

// With local variable
const myElement = document.getElementById('myElement'); = 'none'; // Access via local variable
myElement.textContent = 'Hello, World!'; // Repeated access via local variable

In the second code block, the DOM is only accessed once, resulting in a potentially significant performance gain. Combine these techniques for efficient DOM access: minimizing access, caching, and using local variables. Implementing these practices will lead to performance gains and a smoother user interaction.

Implementing efficient DOM updates

First things first, let's take a moment to contemplate the majesty of batching updates for smoother DOM manipulation. As you well know, we can easily find ourselves making small updates to the DOM ad nauseam in response to user input, altering bits of text or shifting styles around. Micro-changes of this sort, though seemingly inconsequential, can unintentionally trigger frequent reflows that grumble and grind your application to a snail's pace. By batching requests, however, we sidestep this sticky wicket and overhaul the DOM en masse, minimizing the overhead of reflows and repaints. Consider the following example:

let updates = [];

// A function to batch our updates
function batchUpdate(update){
    if(updates.length === 1){
        setTimeout(runUpdates, 0);

// A function to run all the batched updates
function runUpdates(){

Next on the agenda, let's talk document fragments. A lesser known tool in the JavaScript toolbox, document fragments serve as a stand-in when we are adding multiple elements to the DOM simultaneously. Instead of direct insertion which causes multiple reflows, we append our elements to the fragments first, make our changes, and then append that fragment to the DOM all at once. Here's how it's done:

// Create a document fragment
const fragment = document.createDocumentFragment();

// Add elements to the fragment
for (let i = 0; i < 100; i++) {
    let newElement = document.createElement('p');
    newElement.textContent = 'Paragraph ' + (i+1);

// Append the fragment to the DOM

Have you ever stopped to ponder about handling CSS classes in a cost-effective manner? This might seem like an insignificant issue, unthinkable to cause any substantial overhead. But, sadly, that's not the case. Manipulating classes can cause reflows and repaints, pulling the brakes on your application's performance. Luckily, the classList API comes to the rescue, providing us with methods such as add(), remove(), and toggle(). To minimize reflows, it’s advisable to make changes to classes in JavaScript and let the browser handle the update in a more optimized manner. Take a peek at this example:

// Add a new class

// Remove an existing class

// Toggle a class

In conclusion, implementing efficient DOM updates in JavaScript is achievable through tactful batching of updates, usage of document fragments when appending multiple elements simultaneously, and optimized handling of CSS classes. These advanced techniques, when applied appropriately, can result in significant performance enhancement of your web applications. Incorporating these strategies into your DOM manipulations will ensure faster page load times, seamless user experiences, and more efficient resource utilization.

Event Management and Delegation

Event handlers are like the sentinels of your web applications, responding swiftly to user actions. However, attaching a multitude of listeners to individual elements can put a strain on your application's performance and lead to suboptimal memory usage. Event delegation, or the practice of attaching a single event listener to a parent element, offers a solution to this problem and significantly improves your application's responsiveness.

// Non-ideal: Individual event handlers for each element
const buttons = document.querySelectorAll('.button');
buttons.forEach((button) => {
  button.addEventListener('click', (event) => {
    // Handle the click event here

In the code block above, each .button is assigned an individual click listener. When even a minimal number of button exist, this setup may not pose a problem. However, in a more dynamic application where elements could be added or removed, and where a large number of such elements may exist simultaneously, this approach would lead to performance degradation.

Small changes in your code can bring about substantial performance boosts. By switching to event delegation, you can attach just one event listener to a parent element that propagates the handling of events for all of its children. Here is an example:

// Better: Event delegation
const body = document.querySelector('body');
body.addEventListener('click', (event) => {
  if ('.button')) {
    // Handle the click event here

In this improved example, a single event listener on the body element handles clicks on all .button elements. This is because the click event bubbles up the DOM from the click's original target; the handler checks if the event's actual target matches the .button class and handles the event if it does. This simple adjustment drastically reduces the number of event listeners in your application, freeing up valuable memory and making your application more responsive.

Beyond performance benefits, event delegation also brings about a level of fluidity in handling dynamic elements. Since the event listener is attached to the parent, newly added elements are instantly covered. Without event delegation, you would need to expressly attach a new event handler each time a new element is added.

Can you envision the overhead of individually managing each event listener in such a case? On the scale of a real-world application, this approach is clearly unsustainable. Always consider the more extensive context and potential savings in performance and memory usage when implementing your event handlers. This will ensure that your application remains performant and responsive under various scales and conditions. Remember, in the world of web application development, every microsecond counts.

Benchmarking and identifying bottlenecks in DOM operations

Profiling and benchmarking your JavaScript code is a necessary step in diagnosing the efficiency and smoothness of your DOM operations. Leveraging tools like Chrome DevTools is especially beneficial in this process. The Performance and Memory tabs in Chrome DevTools are instrumental in pinpointing areas of your code that are resource-demanding or causing performance bottlenecks. Profiling with the Performance tab affords you the ability to time the execution of your code, an advantage that becomes apparent in intricate applications that indulge in extensive DOM manipulation. Concurrently, the Memory tab sheds light on how memory is being managed by your application, a crucial factor for detecting and rectifying memory leaks and inefficiencies.

The process of optimizing the identified bottlenecks is tantamount to boosting the efficiency of your JavaScript code and maintaining peak application performance. Pay special attention to the profiling results, as they will guide the optimization process. Ensure you are continuously profiling your code and consider each iteration a learning opportunity. Your code can always be fine-tuned or adjusted to achieve the best results tailored for your specific application.

To make the most of your optimization efforts, your focus should be not only on DOM operations. All aspects of your web development practice are interconnected, and tweaking one area can impact the other. Therefore, a comprehensive approach that takes into account all facets of your application should be your guiding philosophy in creating a streamlined and optimized web application.

Moreover, the practice of benchmarking your code should not be overlooked, particularly for critical segments. Though it might be executed less often than profiling, benchmarking plays a vital role in the overall optimization process. With tools like Lighthouse, you are able to assess your application's performance and receive valuable recommendations for enhancements. The execution time of your code, accurately measured through benchmarking, will reveal the efficacy of the modifications you've introduced based on profiling. It truly illuminates whether your refined code has led to increased efficiency.


In this article, the author explores best practices for efficient and smooth DOM operations in JavaScript. They cover topics such as reducing and optimizing DOM access, implementing efficient DOM updates, event management and delegation, and benchmarking and identifying bottlenecks in DOM operations. The key takeaways include caching frequently accessed elements, using local variables to reference DOM nodes, batching updates for smoother manipulation, using document fragments when adding multiple elements, optimizing handling of CSS classes with the classList API, and event delegation for improved performance. The challenging technical task for the reader is to analyze their own codebase and identify opportunities for optimizing DOM operations, implementing the discussed best practices.

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