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What is the Document Object Model (DOM)?

From: JavaScript: Enhancing the DOM

Video: What is the Document Object Model (DOM)?

Before we get started we need to talk about: what the DOM is, why its important, and discuss some DOM related terminology. The DOM is and acronym for Document Object Model. Its job is to describe the structure of a HTML document and the relationship between different elements like tags, attributes, and texts on a page. As you add, delete or modify existing elements on your website, you're creating structure that a browser interprets as the DOM. So, if I go to this page and I add a new navigational element.

What is the Document Object Model (DOM)?

Before we get started we need to talk about: what the DOM is, why its important, and discuss some DOM related terminology. The DOM is and acronym for Document Object Model. Its job is to describe the structure of a HTML document and the relationship between different elements like tags, attributes, and texts on a page. As you add, delete or modify existing elements on your website, you're creating structure that a browser interprets as the DOM. So, if I go to this page and I add a new navigational element.

(SOUND). Then I'm adding an additional node to this page's DOM. This node has different relationships, like siblings and parents. So, the other li elements on this list are the siblings of the new node I just created. The ol tag is it's parent. The DOM is also the API that gives languages like JavaScript and CSS a way to define and modify the existing document. So, I have an article tag here with an id of main as well a headline right underneath. If I go to the CSS with this document I can access that element each 1 node and ask the browser to change it's color. The browser knows how to access this element, because it looks at the HTML I wrote, and creates a DOM tree.

Once that structure exists, it can can map the CSS I wrote and target a specific element in the page. It's really best to think of the DOM as an upside down family tree. I'm working with a really simple webpage with a traditional HTML structure plus a header, an article tag, and a footer. At the top of the family tree is the document itself. And then what we called a root element, which is normally the HTML tag. Inside that element, we have children of the html element, which is normally the head and the body tags. Inside those, we may have some additional elements.

For example, in the head section, we may have a title element, a script tag, and maybe a call to an external style sheet. Inside the body tag we may have a header, and that header can have a nav, and that nav can have a list of links. Each one of those links may have an anchor tag inside them. We could also have an article tag, with a series of headlines and paragraphs.

Every element in the DOM, including the text and attributes are considered nodes. Nodes can be both parent, and have children elements. But they can also have other relationships. Elements in the same level is known as siblings. So these h1 and paragraph tags are considered siblings. So are these li tags. Siblings are elements with the same parents. The first and last children of an element have special names called first child and last child. The rest of the children of the element are known as child nodes. Remember that browsers use your HTML code to create this DOM structure. And this is why it's really important to write clean and valid HTML. So that your CSS and JavaScript code can access and modify existing elements without any problem.

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This video is part of

Image for JavaScript: Enhancing the DOM
JavaScript: Enhancing the DOM

36 video lessons · 7643 viewers

Ray Villalobos
Author

 
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  1. 2m 36s
    1. Welcome
      59s
    2. What you should know before watching this course
      50s
    3. Using the exercise files
      47s
  2. 24m 33s
    1. What is the Document Object Model (DOM)?
      3m 2s
    2. Navigating the DOM with developer tools
      8m 10s
    3. Testing JavaScript commands with the console
      5m 50s
    4. Communicating with the console through JavaScript
      7m 31s
  3. 31m 9s
    1. Selecting elements with getElementById
      4m 10s
    2. Choosing elements by HTML tag
      3m 20s
    3. Isolating elements by class name
      3m 12s
    4. Querying CSS to select elements
      4m 54s
    5. Working with named form elements
      3m 39s
    6. Understanding nodeType, nodeName, and nodeValue
      4m 30s
    7. Traversing up and down DOM nodes
      4m 40s
    8. Targeting node elements
      2m 44s
  4. 22m 25s
    1. Changing HTML attributes
      5m 25s
    2. Working with restricted attributes
      2m 49s
    3. Detecting data attributes
      3m 29s
    4. Controlling classes with the HTML5 classList
      3m 21s
    5. Targeting the attributes property
      1m 24s
    6. Using text content modifiers
      3m 42s
    7. Modifying elements as text
      2m 15s
  5. 14m 57s
    1. Creating and appending nodes
      4m 27s
    2. Controlling node insertions with insertBefore
      3m 17s
    3. Cloning and removing nodes
      4m 41s
    4. Replacing existing nodes
      2m 32s
  6. 26m 14s
    1. What we'll build
      2m 16s
    2. Adding a bubbling event listener
      4m 11s
    3. Creating and styling an overlay with JavaScript
      4m 39s
    4. Adding an image
      3m 48s
    5. Resizing images in the DOM
      2m 59s
    6. Centering an image
      2m 36s
    7. Handling clicks
      1m 29s
    8. Adjusting for scrolling
      1m 36s
    9. Detecting and adjusting for a window resize
      2m 40s
  7. 1m 49s
    1. Next steps
      1m 49s

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