DevVoltz Academy | Understanding the DOM

Part 3: Understanding the DOM

What is the DOM?

Document Object Model

DOM

DOM Definition

The Document Object Model (DOM) is a programming interface for web documents.

It represents the structure of a document as a tree of objects
It allows programs to manipulate the document's structure, style, and content
The DOM represents the document as nodes and objects
It's a W3C (World Wide Web Consortium) standard

API

DOM as an API

The DOM is an Application Programming Interface (API)

It provides a structured representation of the document
It defines how that structure can be accessed and manipulated
It connects web pages to scripts or programming languages
Most commonly used with JavaScript

BRIDGE

Why DOM Matters

The DOM is essential for dynamic web pages

It enables JavaScript to interact with HTML and CSS
It allows for dynamic content updates without page reloads
It's the foundation for modern web applications
It enables event handling and user interactions

Part 3: Understanding the DOM

DOM Tree Structure

Hierarchical Representation of Documents

sample.html

<!DOCTYPE html>
<html>
<head>
  <title>My Page</title>
</head>
<body>
  <h1>Hello World</h1>
  <p>This is a paragraph</p>
  <div>
    <span>Nested element</span>
  </div>
</body>
</html>

DOM Tree

Document

html

head

title

body

div

span

Key Points About the DOM Tree:

Hierarchical Structure

Elements are organized in a parent-child relationship

Node Types

Different types of nodes: element, text, attribute, etc.

Root Node

The document node is the root of the DOM tree

Traversal

You can navigate through parent, child, and sibling nodes

Part 3: Understanding the DOM

How Browsers Interpret HTML

From HTML to DOM to Render Tree

HTML Parsing

The browser reads the HTML and creates tokens that are converted into nodes

DOM Construction

Nodes are organized into a tree structure - the Document Object Model

CSS Parsing

CSS is parsed and styles are applied to the DOM nodes

Render Tree

A render tree is created combining DOM and CSSOM (CSS Object Model)

Layout

The browser calculates the exact position and size of each element

Painting

The browser paints the pixels to the screen

NOTE

JavaScript execution can block DOM construction if not handled properly (using async/defer attributes)

Part 3: Understanding the DOM

DOM Nodes vs Elements

Understanding the Building Blocks

DOM Nodes

Base Interface

All objects in the DOM implement the Node interface

Multiple Types

Element, Text, Comment, Document, etc.

Properties

nodeName, nodeType, nodeValue, childNodes, etc.

Methods

appendChild(), removeChild(), cloneNode(), etc.

Hierarchy

Organized in parent-child-sibling relationships

DOM Elements

Specific Type

Elements are a specific type of Node (nodeType = 1)

HTML Tags

Represent HTML tags like <div>, <p>, <span>

Properties

id, className, innerHTML, style, attributes, etc.

Methods

getAttribute(), setAttribute(), querySelector(), etc.

Manipulation

Can be created, modified, or removed dynamically

Common DOM Node Types:

Element (1) Attribute (2) Text (3) Comment (8) Document (9) DocumentType (10)

Part 3: Understanding the DOM

DOM Manipulation Demo

Interacting with the DOM using JavaScript

Change Text

Add New Element

Change Color

Remove Element

This is the original content. Click the buttons above to see DOM manipulation in action!

JavaScript DOM Methods Used:

Selecting Elements

document.getElementById('demoResult')
document.querySelector('.interactive-element')
document.querySelectorAll('p')

Modifying Content

element.innerHTML = 'New content'
element.textContent = 'Text only'
element.style.color = 'red'

Creating/Removing Elements

document.createElement('div')
parent.appendChild(newElement)
element.remove()

Event Handling

element.addEventListener('click', function() {
// Handle click event
})

Part 3: Understanding the DOM

Inspecting the DOM

Using Browser Developer Tools

How to Inspect the DOM in Your Browser:

1. Open Developer Tools

Right-click on any element and select "Inspect" or press F12

2. Elements Panel

View the DOM tree in the Elements/Inspector tab

3. Navigate the Tree

Click on elements to expand/collapse and see their properties

4. Modify in Real-time

Double-click on text or attributes to edit them directly

5. Console Access

Use the Console tab to run JavaScript commands on the DOM

Pro Tips for DOM Inspection:

🔍

Use the element selector tool to quickly find elements

🔄

Right-click any element and select "Break on" for debugging

📊

Check the Computed tab to see final CSS values

🎯

Use $0 in Console to reference the currently selected element

COMPLETE

Excellent Work!

You've mastered DOM Fundamentals

What We Covered in Part 3:

DOM

What is DOM

Document Object Model basics

TREE

DOM Tree Structure

Hierarchical representation

BROWSER

Browser Rendering

How browsers process HTML

NODES

Nodes vs Elements

DOM building blocks

MANIPULATION

DOM Manipulation

Changing content dynamically

INSPECT

DOM Inspection

Using developer tools

Practice Exercise:

Create an Interactive To-Do List

Using DOM manipulation, create a to-do list where you can:

Add new tasks
Mark tasks as completed
Remove tasks
Filter tasks (all, active, completed)

Next: Learn about event delegation, performance optimization, and modern DOM APIs

Presenter Notes - Video 3

Intro Slide: Emphasize that the DOM is the bridge between static HTML and dynamic JavaScript. It's what makes modern web applications possible.

What is DOM: Explain that the DOM is not part of JavaScript - it's a separate API that JavaScript can access. Use the analogy of a family tree to explain the DOM structure.

DOM Tree: Show the relationship between HTML nesting and DOM hierarchy. Demonstrate with a simple HTML page in browser dev tools.

Browser Rendering: Explain the critical rendering path. Mention that JavaScript can block rendering if not handled properly.

Nodes vs Elements: Clarify that all elements are nodes, but not all nodes are elements. Show examples of different node types in dev tools.

DOM Manipulation: Live code the demo. Show how to select elements and modify them. Emphasize the difference between innerHTML and textContent.

Inspecting DOM: Do a live demonstration of browser dev tools. Show how to inspect elements, modify CSS, and use the console for DOM manipulation.

Recap: Summarize key concepts. Assign the to-do list exercise. Preview event handling and performance topics for next video.

Understanding the DOM Document Object Model Web Interactivity

Simegnew Destew

What is the DOM?

DOM Definition

DOM as an API

Why DOM Matters

DOM Tree Structure

Key Points About the DOM Tree:

Hierarchical Structure

Node Types

Root Node

Traversal

How Browsers Interpret HTML

HTML Parsing

DOM Construction

CSS Parsing

Render Tree

Layout

Painting

DOM Nodes vs Elements

DOM Nodes

Base Interface

Multiple Types

Properties

Methods

Hierarchy

DOM Elements

Specific Type

HTML Tags

Properties

Methods

Manipulation

Common DOM Node Types:

DOM Manipulation Demo

JavaScript DOM Methods Used:

Selecting Elements

Modifying Content

Creating/Removing Elements

Event Handling

Inspecting the DOM

How to Inspect the DOM in Your Browser:

1. Open Developer Tools

2. Elements Panel

3. Navigate the Tree

4. Modify in Real-time

5. Console Access

Pro Tips for DOM Inspection:

Excellent Work!

What We Covered in Part 3:

What is DOM

DOM Tree Structure

Browser Rendering

Nodes vs Elements

DOM Manipulation

DOM Inspection

Practice Exercise:

Create an Interactive To-Do List

Presenter Notes - Video 3