Performance considerations when manipulating the DOM

Anton Ioffe - November 6th 2023 - 8 minutes read

As a proficient JavaScript developer, you're no stranger to manipulating the DOM, yet are you doing it most efficiently? Welcome to our deep dive into "JavaScript and the DOM: A Guide to Performance Optimization". In this comprehensive exploration, we'll peel back the layers of JavaScript DOM manipulation, illuminating how access methods, element properties, and even your approach to monitoring can drastically impact performance. Harnessing performance potential isn't just about spotting the problem; it's about leveraging cutting-edge solutions and best practices to catapult your user experience to the next level. Get ready to examine real-world examples, case studies, and tangible, implementable techniques to turn your DOM know-how into a masterclass of performance optimization. Stay tuned, as this journey takes us from foundations of performance to the front lines of development!

Performance Basics in JavaScript DOM Manipulation

JavaScript's interaction with the Document Object Model, or DOM, plays a pivotal role in enabling interactive and responsive web pages. JavaScript turns a web document into a tree-like structure of objects called nodes, each one representing an HTML element. These nodes can then be manipulated dynamically, with operations ranging from changing content and style to responding to user interactions. Having a masterful handle of these operations allows developers to create fluid interfaces that enhance user experience.

Performance in DOM manipulation is crucial. Every time a DOM operation occurs, it leads to a change in the state of the webpage, causing reflows and repaints. The browser has to recalculate the layout from scratch, which leads to time-consuming rendering processes that can negatively affect overall web performance. Excessive DOM manipulation can substantially slow down web page rendering, creating a lag that chips away at the user experience.

While the DOM operations themselves are lightweight, a cascade of re-rendering triggered by frequent data changes can be quite costly, resulting in significant degradation of webpage performance. Therefore, it's advisable to minimize unnecessary DOM updates as much as possible. This involves carrying out as many changes as possible in one go rather than triggering continuous updates. Batching updates not only reduces the number of render cycles but also lowers the overall cost of re-rendering.

Consider leveraging browser APIs that allow for efficient batch operations on the DOM, such as 'document fragments'. These act as temporary containers for new nodes, enabling you to make multiple changes offline before appending them to the DOM - all in one operation. This synergy of JavaScript and the DOM, optimized toward minimizing reflows and repaints, results in noticeably better web performance. By ensuring the maintenance of a responsive interface even during data-intensive operations, you offer a superior, seamless user experience.

Understanding DOM Access and Element Properties in Performance Optimization

DOM manipulation in JavaScript largely revolves around accessing and modifying elements. These tasks form the architecture for interactive web design, but if not efficiently managed, can negatively impact performance.

Accessing DOM Elements Accessing elements within the DOM can be done with JavaScript through a variety of specific methods. For instance, getElementById, querySelector, and querySelectorAll are a few commonly utilized functions. getElementById retrieves an element by its unique id attribute, while querySelector and querySelectorAll enable you to retrieve elements based on CSS selectors, fetching only the first match and all matches respectively.

When considering performance, we can access DOM elements in the least cost-intensive way by using their id attribute with getElementById:

var elem = document.getElementById('myElementId');

Compared to the querySelector method, this approach is faster since it directly accesses the element through its unique identifier. Using querySelector involves more complex computation as it executes CSS selection matching which can lead to slower performance if not properly optimized.

Modifying DOM Elements Once the elements are accessed, JavaScript allows us to modify them dynamically through various properties and events. Properties are used for changing element content, updating attributes, inserting new elements, or even removing existing ones from the DOM.

For instance, you can change the content of a HTML tag using the innerHTML or textContent properties:

elem.textContent = 'New content'; //Changes only the text content
elem.innerHTML = '<span>New content</span>'; // Changes the complete HTML within the element

Keep in mind that while innerHTML provides more flexibility, it's more process-intensive as it needs to parse raw HTML strings into DOM nodes, interacting with the rendering engine of the browser. Therefore, if you are making simple changes to the text, utilizing textContent would offer better performance.

Remember, accessing and changing DOM elements can have considerable performance implications if not managed properly. Do ask yourself, have you optimized how you're interacting with the DOM? Are you using the most efficient methods to access and manipulate your webpage's elements? The end goal should always be to provide a seamless user experience without sacrificing performance.

Monitoring Performance: Identifying and Analyzing Performance Leaks

Identifying performance leaks in your JavaScript can be a crucial step in optimizing your application. One common culprit is excessive interaction with the DOM. Fewer interactions with the DOM result in fewer re-renders, improving performance. Always consider whether frequent manipulations are necessary or if changes can be compiled and made in a single interaction. For instance, the use of document.createDocumentFragment() can significantly reduce re-renders, as modifications are made off-screen and only put into the actual DOM once, leading to a smoother user experience.

var frag = document.createDocumentFragment(),
    list = document.getElementById('myList'),
    items = ['Apple', 'Orange', 'Banana', 'Mango'];

items.forEach(function(item) {
    var li = document.createElement('li');
    li.textContent = item;


Event handling can also contribute to inefficient performance. As an example, frequently triggering events resulting from user interactions can lead to performance issues. A more efficient approach would be delegating event listeners to a common parent, reducing the number of event listeners wired up in the DOM. This saves memory and improves performance, especially when dealing with a large number of similar elements.

// Bad practice: Add event listener to each button
var buttons = document.querySelectorAll('button');
buttons.forEach(function(button) {
    button.addEventListener('click', function() {
        console.log('Button clicked!');

// Good practice: Use event delegation
document.body.addEventListener('click', function(e) {
    if( === 'BUTTON') {
        console.log('Button clicked!');

Memory leaks are another form of performance leaks to observe. These leaks occur due to unused or uncleaned resources which hold onto memory, leading to increased consumption over time. Periodically check your application looking for unusual or unexpected increases in memory usage. Tools like Chrome's Memory Profiler can be helpful for this. In JavaScript, ensure all references to unused objects are deleted or nulled so that they can be garbage-collected.

// Example of memory leak
var memoryLeak = function() {
    var largeStr = new Array(2000000).join('memoryLeak');
    return function() {

setTimeout(memoryLeak, 1000);

// Avoiding memory leak
var avoidMemoryLeak = function() {
    var largeStr = new Array(2000000).join('avoidMemoryLeak');
    return function() {
        largeStr = null;  // Allow garbage collection

setTimeout(avoidMemoryLeak, 1000);

Understanding how to identify and handle these performance leaks can be the difference between a sluggish and a smooth web application. Always strive to effectively manage DOM interactions, use optimal event handling, and regularly check for possible memory leaks to ensure high performance. Forethinking these considerations and incorporating efficient practices can significantly enhance your JavaScript application's performance.

What could be an effective strategy for identifying potential points of memory leaks in your codebase? Have you ever encountered a scenario where unoptimized event handling had a significant impact on your application's performance?

Improving Performance: Techniques and Best Practices

The first point to consider when aiming for an optimized performance in DOM manipulation is to minimize unnecessary reflows and repaints. Reflow refers to the browser's process of recalculating the layout of the DOM while repaint is when the browser updates the pixels on-screen. Excessive reflows and repaints can significantly degrade the performance as they are time-consuming processes. Instead, aim to batch style changes and avoid interspersing reading and writing to the DOM layout properties.

const exampleElement = document.getElementById('exampleId'); = 'block'; // Interspersed reading and writing
const display = getComputedStyle(exampleElement).display; = display === 'block' ? 'none' : 'block';

The second practice is using document fragments when you need to make multiple changes to the DOM. Instead of making each change directly on the live DOM, it is far more efficient to use a document fragment. This represents a minimal document object without any parent reference, which enables appending multiple nodes without causing reflows.

const list = document.querySelector('ul');
const docFragment = document.createDocumentFragment();

['Item 1', 'Item 2', 'Item 3'].forEach(itemText => {
    const li = document.createElement('li');
    li.textContent = itemText;

list.appendChild(docFragment); // Single reflow

Third, avoid constant direct DOM manipulation. Each time JavaScript modifies the DOM, the browser must recalculate the layout and repaint the screen. Limiting these operations can bring noticeable performance improvement. Techniques like event delegation or throttling input events prove to be useful in controlling direct DOM manipulation.

// Instead of attaching event listeners to each button
document.querySelectorAll('button').forEach(button => {
    button.addEventListener('click', handleClick);

// Use event delegation
document.body.addEventListener('click', event => {
    if ( === 'BUTTON') {

Finally, leveraging the benefits of Virtual DOM can remarkably boost the performance. A JavaScript concept, Virtual DOM allows changes to be made and held in a JavaScript object, which is then compared with the real DOM. Only the changes are then updated in the real DOM, reducing the need for expensive DOM operations.

// React example using Virtual DOM 
function ExampleComponent() {
    const [counter, setCounter] = React.useState(0);

    return (
            Count: {counter}
            <button onClick={() => setCounter(counter + 1)}>

By employing these techniques, you can effectively improve the performance of JavaScript applications resulting from DOM manipulations. What other techniques do you know for improving the performance of DOM manipulation in JavaScript? Does the nature of your project affect your choice of technique?

Case Study: Real-world Performance Considerations when Manipulating the DOM

In our case study, we'll examine a call tracking dashboard application built with JavaScript. The app includes multiple filters, a dynamic table, and charts, with the data updated in real-time. Over time, the app began to slow down, especially when dealing with large volumes of data. The prime suspect was excessive DOM manipulation, which can drastically affect a web application's performance.

Diving into the application code, we indeed found multiple instances of direct DOM manipulation. Specifically, there were many operations inserting, updating, and deleting data in the table and charts directly on the DOM. These operations were not optimized as they were causing the browser to re-render the DOM tree and recalculate layout after each operation. In addition, a new fetch request was made every time a DOM update was initiated, leading to a convoluted sequence of updates that left the user interface stuttering.

To rectify these performance issues, we implemented a few strategically chosen techniques. First, we ensured that data fetches were asynchronous. We used the fetch API and async/await syntax to provide an easy-to-use, promise-based mechanism for handling asynchronous operations. This way, we maintained a responsive user interface even when dealing with backend server requests.

Next, we minimized direct DOM manipulation by batching updates. Rather than updating the DOM for each new piece of data, we used document fragments to compile a group of updates before appending them to the DOM. By making these changes, our dashboard application became significantly faster, even with substantial volumes of data. The tool no longer suffered from lagging or unresponsive interactions, and the user experience was vastly improved.


In this article on performance considerations when manipulating the DOM in JavaScript, the author emphasizes the importance of optimizing DOM operations to enhance web performance. They discuss techniques such as batching updates using document fragments and efficient DOM access methods. The article also covers monitoring performance, identifying and handling performance leaks, and improving performance through best practices. The key takeaway is that by implementing these techniques, developers can significantly improve the performance of their JavaScript applications. As a challenging technical task, the reader is encouraged to analyze their own codebase for potential points of memory leaks and unoptimized event handling that could impact their application's performance.

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