Introduction to the DOM
The power of JavaScript is its use in dynamically displaying and manipulating elements on a webpage written in HTML. We know that an HTML page consists of elements such as <head><body> <h1> tags or text fields and buttons. The DOM or Document Object Model represents the structure of these elements as a "tree" data structure after your web browser reads a page. The DOM Application Programming Interface (API) contains methods that provide JavaScript access to these elements. Start by reading this article to learn about the document structure of the DOM and how to find, create and change elements.
Think back to the syntax trees. Their structures are strikingly similar to the structure of a browser's document. Each node may refer to other nodes, children, which in turn may have their own children. This shape is typical of nested structures where elements can contain subelements that are similar to themselves.
We call a data structure a tree when it has a branching structure, has no cycles (a node may not contain itself, directly or indirectly), and has a single, well-defined root. In the case of the DOM, document.documentElement serves
as the root.
Trees come up a lot in computer science. In addition to representing recursive structures such as HTML documents or programs, they are often used to maintain sorted sets of data because elements can usually be found or inserted more efficiently in a tree than in a flat array.
A typical tree has different kinds of nodes. The syntax tree for the Egg language had identifiers, values, and application nodes. Application nodes may have children, whereas identifiers and values are leaves, or nodes without children.
The same goes for the DOM. Nodes for elements, which represent HTML tags, determine the structure of the document. These can have child nodes. An example of such a node is document.body. Some of these children can be leaf nodes, such as pieces
of text or comment nodes.
Each DOM node object has a nodeType property, which contains a code (number) that identifies the type of node. Elements have code 1, which is also defined as the constant property Node.ELEMENT_NODE.
Text nodes, representing a section of text in the document, get code 3 (Node.TEXT_NODE). Comments have code 8 (Node.COMMENT_NODE).
Another way to visualize our document tree is as follows:
The leaves are text nodes, and the arrows indicate parent-child relationships between nodes.