
Most of the Javascript frameworks like Vue, React and Ember implement a “virtual DOM”.
While it seems like some thing from a technological know-how fiction, its number one motive for present is to expand the speed and proficiency of DOM updates. It offers a few more advantages as well.
What the DOM actually is (a reminder)
We have a tendency consider the DOM as the HTML document it represents. but without a doubt the DOM is a tree-like data structure that comes into existence as soon as an HTML document has been parsed
The browser paints the DOM to the screen and will repaint it inresponse to user actions (e.g. mouse clicks) and updates through its API from your Javascript scripts e.g. document.createElement.
It’s expensive to update the DOM
When we use Javascript to make a change to our page, the browser has to do some work to find the required DOM nodes and make the change e.g.
// #myId could be anywhere in the document, which may have thousands of nodes! document.getElementById('myId').appendChild(myNewNode);
In modern apps there can be thousands of nodes in the DOM, and so updates can be computationally expensive. It’s inevitable that small, frequent updates will slow the page down.
What is a virtual DOM?
The DOM can be represented as a data structure in Javascript, too. Here is pseudo-code of ways a DOM node may be represented:
// An unordered list represented as Javascript let domNode = { tag: 'ul', attributes: { id: 'myId' }, children: [ // where the LI's would go ] };
If we call that a “virtual” DOM node, then the complete structure of DOM nodes would make up our virtual DOM.
But why do this?
It’s not very expensive to update virtual nodes.
// This might be how we update the virtual DOM domNode.children.push('
- Item 3
');
If we use a virtual DOM, in preference to our code directly calling the DOM API with methods like .getElementById to make updates, the code will make adjustments just to the JS object, which is cheap.
Then, whilst it’s time to get the real DOM in sync with the modifications we’ve made, an efficient updating function is used:
// This function would call the DOM API and make changes // to the browser's DOM. It would do it in batches and with // more efficiency than it would with arbitrary updates. sync(originalDomNode, domNode);
In any one cycle there may be many nodes to update, so batching API calls in this way could reduce a lot of inefficiency.
More than performance
Having a virtual DOM it not just a performance enhancement, it means additional functionality will be possible.
For example, in Vue.js, we can bypass the need for an HTML template or a template property by using a render() method, which returns virtual nodes:
new Vue({ el: '#app', data: { message: 'hello world' }, render(createElement) { return createElement( 'div', { attrs: { id: 'myId' } }, this.message ); } });
Output:
<div id='app'> <div id='myId'>hello world</div> </div>
Why do that? There are several viable benefits:
- You get the programmatic strength of Javascript. you could create factory-style functions to build your virtual nodes using Javascript’s array methods etc, something that might be more difficult using template syntax.
- You may make your code universal. since your Vue instance does not really on an HTML file it is also renderable by a server for server-side rendering.
- JSX. Render functions allow JS extensions like JSX which may be acceptable for architecting a component-based app.
Note: this article was originally posted here on the Vue.js Developers blog on 2017/02/21

Janeth Kent
Licenciada en Bellas Artes y programadora por pasión. Cuando tengo un rato retoco fotos, edito vídeos y diseño cosas. El resto del tiempo escribo en MA-NO WEB DESIGN AND DEVELOPMENT.
Related Posts
How to use the endsWith method in JavaScript
In this short tutorial, we are going to see what the endsWith method, introduced in JavaScript ES6, is and how it is used with strings in JavaScript. The endsWith method is…
What are javascript symbols and how can they help you?
Symbols are a new primitive value introduced by ES6. Their purpose is to provide us unique identifiers. In this article, we tell you how they work, in which way they…
Callbacks in JavaScript
Callback functions are the same old JavaScript functions. They have no special syntax, as they are simply functions that are passed as an argument to another function. The function that receives…
How to create PDF with JavaScript and jsPDF
Creating dynamic PDF files directly in the browser is possible thanks to the jsPDF JavaScript library. In the last part of this article we have prepared a practical tutorial where I…
How to make your own custom cursor for your website
When I started browsing different and original websites to learn from them, one of the first things that caught my attention was that some of them had their own cursors,…
Node.js and npm: introductory tutorial
In this tutorial we will see how to install and use both Node.js and the npm package manager. In addition, we will also create a small sample application. If you…
How to connect to MySQL with Node.js
Let's see how you can connect to a MySQL database using Node.js, the popular JavaScript runtime environment. Before we start, it is important to note that you must have Node.js installed…
JavaScript Programming Styles: Best Practices
When programming with JavaScript there are certain conventions that you should apply, especially when working in a team environment. In fact, it is common to have meetings to discuss standards…
Difference between arrow and normal functions in JavaScript
In this tutorial we are going to see how arrow functions differ from normal JavaScript functions. We will also see when you should use one and when you should use…
JavaScript Arrow functions: What they are and how to use them
In this article we are going to see what they are and how to use JavaScript Arrow Functions, a new feature introduced with the ES6 standard (ECMAScript 6). What are Arrow…
How to insert an element into an array with JavaScript
In this brief tutorial you will learn how to insert one or more elements into an array with JavaScript. For this we will use the splice function. The splice function will not…
What is the difference between primitives types and objects in JavaScript?
In this short tutorial we are going to look at the differences between primitive types and objects in JavaScript. To start with, we're going to look at what primitive types…