1️⃣1️⃣ 📚 XML DOM References & Definitions

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📄 DOM Document – The Root of the XML and HTML DOM Tree

🧲 Introduction – Why Learn About the DOM Document Object?

The Document object is the root node of every XML or HTML DOM tree. It serves as the entry point for accessing and manipulating the entire structure. Whether you’re building a web application, parsing XML in the browser, or using JavaScript to create elements dynamically, everything starts from the DOM Document.

🎯 In this guide, you’ll learn:

What the DOM Document is and why it matters
How to access and manipulate elements using document
Common methods like createElement, getElementById, and querySelector
How XML DOM differs slightly from HTML DOM

📘 What Is the DOM Document?

The Document node is the top-level node (nodeType = 9) that represents the entire XML or HTML document. It gives you access to:

Root elements
Metadata like DOCTYPE
Global search methods
DOM creation and parsing tools

✅ In browsers, the global document object refers to the HTML or XML document currently loaded.

🧾 Example – HTML/JS Access

<!DOCTYPE html>
<html>
  <head><title>My Page</title></head>
  <body>
    <div id="welcome">Hello, DOM!</div>

    <script>
      const root = document;
      console.log(root.nodeType); // 9 (DOCUMENT_NODE)
      console.log(root.getElementById("welcome").textContent); // Hello, DOM!
    </script>
  </body>
</html>

📄 Example – XML DOM Document (JavaScript)

<library>
  <book id="1">
    <title>XML Mastery</title>
  </book>
</library>

JavaScript:

const parser = new DOMParser();
const xmlDoc = parser.parseFromString(xmlString, "text/xml");

console.log(xmlDoc.nodeType); // 9
console.log(xmlDoc.documentElement.nodeName); // library

🔧 Common Methods of the Document Object

Method	Purpose
`getElementById(id)`	Returns element with the given ID
`getElementsByTagName(tag)`	Returns NodeList of elements by tag
`getElementsByClassName()`	Returns elements with specified class (HTML)
`querySelector()`	Returns the first element matching selector
`querySelectorAll()`	Returns all elements matching selector
`createElement(tag)`	Creates an empty element node
`createTextNode(text)`	Creates a new text node
`createAttribute(name)`	Creates a new attribute node
`createDocumentFragment()`	Creates a lightweight, standalone document
`importNode(node, deep)`	Clones a node from another document
`adoptNode(node)`	Transfers a node from another document

📐 Properties of `Document`

Property	Description
`documentElement`	The root element (e.g., `<html>`, `<library>`)
`childNodes`	Nodes directly under `Document`
`doctype`	The DOCTYPE declaration (`<!DOCTYPE html>`)
`location`	URL of the document (in browsers)
`readyState`	Load state of the document (`loading`, `complete`)

🧠 Use Cases

📥 Parsing and traversing XML documents
🧾 Dynamic DOM creation for web interfaces
🧪 Testing or validating XML/HTML structure
⚙️ JavaScript-based rendering (SSR, client-side templates)
🌐 API response parsing (AJAX + XML)

✅ Best Practices with DOM Document

✔️ Use document.documentElement to get the root node
✔️ Use createElement() and appendChild() to build new DOM trees
✔️ Validate XML documents with tools like DOMParser
✔️ Use querySelector for concise element selection
❌ Don’t manipulate DOM before it’s fully loaded (DOMContentLoaded)
❌ Avoid polluting the global document if working with iframe or XMLDocument

📌 Summary – Recap & Next Steps

The DOM Document object is the gateway to the entire DOM structure, whether for XML or HTML. It provides essential methods for navigating, querying, and building the document tree programmatically.

🔍 Key Takeaways:

document is the root node (nodeType = 9)
It provides methods to search, create, and modify the DOM
Used extensively in both web development and XML processing

⚙️ Real-world relevance: Used in web apps, XML editors, browser extensions, AJAX-based scripts, and dynamic rendering engines.

❓ FAQs – DOM Document

❓ What is the nodeType of document?
✅ 9 – DOCUMENT_NODE

❓ How do I get the root element?
✅ Use document.documentElement

❓ Is the document object the same in HTML and XML?
✅ Mostly. XML documents use DOMParser to create a Document, HTML uses the browser’s built-in document.

❓ How can I parse a string of XML?
✅ Use DOMParser.parseFromString(xmlString, "text/xml").

❓ How can I create a detached DOM tree?
✅ Use document.createDocumentFragment().

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