Understanding the Document Object Model (DOM): A simple definition for Web developers

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Document Object Model (DOM)

Le Document Object Model (DOM) is an essential concept in the web developmentwhich can be used to modify, create and interact with elements on a page HTML or XML. In this article, we will define the DOM and explain how it works.

What is the Document Object Model (DOM)?

Le DOM is a structured representation of an HTML or XML document in the form of a tree of objects, where each object represents a part of the document (for example, an HTML element such as <p> or <div>). This object tree provides developers with a standardised programming interface (API) enabling them to manipulate and modify the content of HTML and XML documents using different programming languages, such as JavaScript.

The DOM object tree

When a web browser loads an HTML or XML document, it creates a tree of objects called a DOM treewhich represents the hierarchical structure of the document. Each node of the DOM tree corresponds to an element of the document, and the relationships between these nodes reflect the logical structure of the document, i.e. the way in which the elements include and relate to each other. Objects in the DOM tree are also called "nodes".

The different types of node in the DOM

The DOM distinguishes between several types of nodes, each with a specific role in the representation of the document:

• • Element : represents an HTML or XML element, defined by an opening tag, any attributes and a closing tag. For example, a <div class=" »exemple »"></div> is an element.
  • Attribute : corresponds to one of the elements which define the characteristics of an element, such as the class, ID or any other custom attribute. In the example above, 'class' is an attribute.

jQuery and the DOM

jQuery is a very popular JavaScript library that simplifies DOM manipulation with a more concise and easy-to-use syntax than the simple native DOM API. This makes selecting and modifying elements much quicker and more intuitive, considerably reducing the complexity of the code and making it easier to read.

Best practice in the French overseas departments

To ensure optimum use of the DOM in your Web projects, here are a few best practices to keep in mind:

• Minimising DOM modifications : Excessive manipulation of the DOM can lead to performance problems, as the browser must constantly re-create the DOM tree and recalculate styles or the layout of elements. We recommend limiting modifications to the DOM and optimising the code that interacts with the elements.
• Using a document fragment : It speeds up operations on the DOM by creating a temporary invisible container to store elements before inserting them into the main DOM tree.
• Making effective selections : Avoid using overly generic selectors such as "getElementsByTagName", which can slow down performance. Instead, opt for faster selectors such as getElementById or querySelector.
• Avoid going back and forth between JavaScript and the DOM : Continuous communication between JavaScript and the DOM can be costly in terms of performance. Instead, try to group DOM manipulations into a single operation wherever possible.

In short, the Document Object Model (DOM) is a hierarchical representation of HTML and XML documents, enabling developers to access, modify and interact with the various elements and attributes of web pages using a standardised API.

By understanding and mastering the principles and tools associated with the DOM, you can create more interactive, dynamic and high-performance Web applications.