DOM

DOM Module

Overview

The DOM (Document Object Model) module provides an in-memory representation of a web document's structure. It implements a tree data structure that mirrors the hierarchical organization of HTML elements.

Purpose

• Store the structural representation of HTML documents
• Maintain element properties, attributes, and content
• Support tree navigation and manipulation
• Provide the foundation for styling and layout operations

Architecture

DOM Tree Structure

The DOM is organized as a tree where:

• Each node represents an HTML element, text content, comment, or the document itself
• Parent-child relationships define the document structure
• Siblings are stored in order to preserve document sequence

Node Types

Type	Purpose	Example
Element	HTML elements	<div>, <p>, <a>
Text	Text content	"Hello World"
Comment	HTML comments	<!-- comment -->
Document	Root of tree	Implicit container

Key Data Structures

Node

Represents a single element in the DOM tree:

• Element data: Tag name, attributes, classes, ID
• Parent reference: Link to parent node
• Children list: Ordered list of child nodes
• Text content: Inner text for text nodes

Attributes

Elements store attributes as key-value pairs:

• id: Unique identifier
• class: CSS class names
• href: Link target (for anchors)
• Custom attributes: Any data attributes

Operations

Tree Navigation

• Get parent node
• Get child nodes
• Get sibling nodes
• Find nodes by selector or criteria

Tree Manipulation

• Add child nodes
• Remove nodes
• Update attributes
• Modify text content

Querying

• Find elements by tag name
• Find elements by class
• Find elements by ID
• Get descendants matching criteria

Integration with Other Modules

Style Module

Uses DOM structure to apply CSS styles and calculate computed properties

Layout Module

Traverses DOM tree to calculate positioning and dimensions

Paint Module

Iterates through DOM to render visible content

JavaScript Module

Provides DOM APIs (getElementById, querySelector, etc.) for script access

Memory Considerations

• Efficient node representation to minimize memory usage
• Shared ownership through reference counting when needed
• Lazy evaluation of properties where possible

Standard Compliance

• Follows W3C DOM specification
• Supports standard DOM methods and properties
• Compatible with CSS selectors for element matching

Example Structure

Document
├── Element: html
│   ├── Element: head
│   │   └── Element: title
│   │       └── Text: "My Page"
│   └── Element: body
│       ├── Element: h1
│       │   └── Text: "Welcome"
│       └── Element: p
│           └── Text: "Hello, world!"

Future Enhancements

• Virtual DOM for efficient updates
• DOM event system
• MutationObserver support
• Performance optimizations for large documents