Day 7: DOM Manipulation in JavaScript
Date: December 14, 2024
Welcome to Day 7 of your JavaScript learning journey! Today’s topic focuses on DOM Manipulation, one of the most exciting aspects of JavaScript. With DOM manipulation, you can dynamically update, add, or remove elements from a webpage, making it interactive and user-friendly. By the end of today’s lesson, you’ll also create a simple To-Do List project to put your knowledge into practice.
1. What is the DOM?
The Document Object Model (DOM) is a programming interface for web documents. It represents the structure of an HTML document as a tree of objects, allowing you to access and manipulate elements programmatically using JavaScript.
Here’s an example of how the DOM represents HTML:
<html>
<body>
<h1>Welcome</h1>
<p>This is a paragraph.</p>
</body>
</html>
The DOM tree for the above would look like this:
Document
└── html
└── body
├── h1
└── p
2. Accessing DOM Elements
You can access elements in the DOM using several methods:
Using getElementById
let title = document.getElementById("title");
console.log(title); // Logs the element with ID "title"
Using getElementsByClassName
let items = document.getElementsByClassName("item");
console.log(items); // Logs all elements with class "item"
Using querySelector and querySelectorAll
let firstItem = document.querySelector(".item"); // First element with class "item"
let allItems = document.querySelectorAll(".item"); // All elements with class "item"
3. Modifying DOM Elements
Changing Content
You can update the text or HTML inside an element using:
- innerText: Updates the visible text.
- innerHTML: Updates the HTML content.
let title = document.getElementById("title");
title.innerText = "Updated Title"; // Changes visible text
title.innerHTML = "<strong>Updated Title</strong>"; // Adds HTML formatting
Changing Styles
You can directly modify the CSS styles of an element.
let title = document.getElementById("title");
title.style.color = "blue";
title.style.fontSize = "24px";
Adding or Removing Classes
let box = document.getElementById("box");
box.classList.add("highlight"); // Adds a class
box.classList.remove("highlight"); // Removes a class
4. Handling Events
Events allow you to make your web pages interactive. Here are some common event types and how to handle them.
Inline Event Handling
In your HTML:
<button onclick="alert('Button Clicked!')">Click Me</button>
Using addEventListener
This approach is preferred as it separates JavaScript from HTML.
let button = document.getElementById("btn");
button.addEventListener("click", function () {
alert("Button Clicked!");
});
Common Events
- click: Triggered when an element is clicked.
- mouseover: Triggered when the mouse hovers over an element.
- keyup: Triggered when a key is released.
Example:
<html>
<body>
<h1>Welcome</h1>
<p>This is a paragraph.</p>
</body>
</html>
5. Project: To-Do List
Let’s combine what you’ve learned into a simple To-Do List application.
HTML Structure
Document
└── html
└── body
├── h1
└── p
How It Works
- User types a task in the input field.
- Clicking "Add Task" creates a new
- element with the task.
- Each task has a "Delete" button to remove it.
6. Key Takeaways
- DOM Access: Use methods like getElementById and querySelector.
- DOM Modification: Change content, styles, and classes dynamically.
- Event Handling: Use addEventListener to make your pages interactive.
- Practice Project: Build a to-do list to reinforce your knowledge.
Practice Tasks for Day 7
- Add a "Mark as Done" feature to your to-do list.
- Create a shopping list app where users can input items and their quantities.
- Experiment with event types like mouseover and keydown in a small project.
Next Steps
Tomorrow, on Day 8, we’ll explore Error Handling and Debugging, learning how to handle unexpected issues in your JavaScript code. See you then!
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