🌐 JavaScript DOM & Browser BOM – Interacting with Web Pages and Browser Environment

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🧲 Introduction – Why Learn DOM & BOM?

Modern web applications are dynamic and interactive. The Document Object Model (DOM) allows JavaScript to interact with HTML elements, update styles, handle user inputs, and create animations. Meanwhile, the Browser Object Model (BOM) gives you access to browser-specific features like alerts, popups, URL redirects, and history management.

🎯 In this guide, you’ll learn:

• How JavaScript interacts with HTML via the DOM
• DOM methods, events, and dynamic changes
• The BOM objects like window, navigator, and location
• Practical usage examples for real-world interactivity

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📘 Topics Covered

🔹 Topic	📄 Description
DOM Elements	Accessing and modifying HTML elements
DOM Forms	Handling form validation and submission
DOM Events	Handling click, input, and custom events
BOM Objects	Working with browser-level APIs
Console Object	Debugging JavaScript in browser console

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🏗️ JavaScript — DOM (Document Object Model)

📌 What is the DOM?

The DOM represents your entire HTML document as a tree-like structure. Each element, attribute, and text node can be accessed and modified using JavaScript.

document.getElementById("title").innerText = "Welcome!";

📋 Accessing Elements

• getElementById()
• getElementsByClassName()
• querySelector() / querySelectorAll()

✏️ Manipulating Elements

const box = document.querySelector(".box");
box.style.backgroundColor = "blue";
box.innerHTML = "<p>Changed Content</p>";

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📝 JavaScript — DOM Forms

You can access forms and fields using:

let username = document.forms["loginForm"]["username"].value;

• Use .addEventListener("submit", ...) to validate before sending
• Access form elements via form.elements[] or input.value

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🌀 JavaScript — DOM Animations

Basic animations can be done via DOM style manipulations:

element.style.transition = "transform 0.5s ease";
element.style.transform = "scale(1.2)";

For advanced effects, consider using requestAnimationFrame() or libraries like GSAP.

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🧭 JavaScript — DOM Navigation

Navigate through DOM hierarchy:

element.parentNode
element.childNodes
element.nextElementSibling

You can traverse to parents, children, or siblings for structured manipulation.

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📚 JavaScript — DOM Methods & Properties

Method/Property	Description
innerHTML	Gets/sets HTML content
textContent	Gets/sets plain text
setAttribute()	Adds/modifies attributes
classList.add() / remove()	Adds/removes class
appendChild() / removeChild()	Adds/removes nodes

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🖱️ JavaScript — Events & addEventListener()

📌 Event Handling Basics

button.addEventListener("click", function() {
  alert("Button clicked!");
});

🧪 Event Delegation

Efficiently handle events using a parent:

document.querySelector("#list").addEventListener("click", (e) => {
  if (e.target.tagName === "LI") {
    console.log("Item clicked:", e.target.textContent);
  }
});

🎯 Custom Events

const customEvent = new CustomEvent("myEvent", { detail: { name: "JS" } });
element.dispatchEvent(customEvent);

Use addEventListener("myEvent", ...) to listen for it.

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🌍 JavaScript — BOM (Browser Object Model)

🪟 Window Object

• Represents the browser window/tab
• Global functions like alert(), setTimeout(), and console.log() belong to it

alert("This is an alert box!");

🌐 Location Object

window.location.href = "https://example.com"; // Redirect
console.log(location.pathname);               // Show current path

📜 History Object

history.back();  // Go to previous page
history.forward(); // Next page

🧭 Navigator Object

console.log(navigator.userAgent);
console.log(navigator.language);

Helps detect browser details.

📤 Popups

window.open("https://example.com", "_blank", "width=600,height=400");

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🧪 JavaScript — Console Object

The console is part of the BOM and used for debugging:

console.log("Debug Info");
console.warn("This is a warning");
console.error("This is an error");

Advanced: Use console.table(), console.group(), and console.time() for structured logs.

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📌 Summary – Recap & Next Steps

The DOM and BOM form the backbone of interactive web pages. Understanding how to select elements, attach event listeners, and work with browser APIs helps you build responsive and user-friendly websites.

🔍 Key Takeaways:

• DOM allows JavaScript to read, write, and manipulate HTML and CSS
• Events help capture and respond to user actions
• BOM enables browser-level interactions (window, history, location)
• Use console for effective debugging

⚙️ Real-World Relevance:
All modern JavaScript frameworks (React, Vue, Angular) abstract the DOM, but understanding it is essential for debugging, performance, and custom scripts.

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❓ FAQs

Q1: What is the DOM used for in JavaScript?

✅ DOM allows JavaScript to read, traverse, and modify the HTML structure and CSS of a web page in real-time.

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Q2: Is window the global object in JavaScript?

✅ Yes, in browsers, window is the global object that contains all variables and functions defined globally.

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Q3: How is the BOM different from the DOM?

✅ DOM represents the HTML page structure; BOM includes browser-level objects like window, navigator, history, etc.

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Q4: Can we create custom events in JavaScript?

✅ Yes, using new CustomEvent() you can dispatch and listen to custom-defined browser events.

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Q5: How to prevent default form submission in JavaScript?

✅ Use event.preventDefault() inside your submit handler.

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