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:
let inputField = document.getElementById("input");
inputField.addEventListener("keyup", function (event) {
console.log(`You typed: ${event.target.value}`);
});
5. Project: To-Do List
Let’s combine what you’ve learned into a simple To-Do List application.
HTML Structure
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>To-Do List</title>
</head>
<body>
<h1>To-Do List</h1>
<input type="text" id="taskInput" placeholder="Enter a task">
<button id="addTaskBtn">Add Task</button>
<ul id="taskList"></ul>
<script src="script.js"></script>
</body>
</html>
JavaScript Code
// Access elements
let taskInput = document.getElementById("taskInput");
let addTaskBtn = document.getElementById("addTaskBtn");
let taskList = document.getElementById("taskList");
// Add event listener to the button
addTaskBtn.addEventListener("click", function () {
let task = taskInput.value; // Get the input value
if (task.trim() !== "") {
// Create a new list item
let listItem = document.createElement("li");
listItem.innerText = task;
// Add a delete button
let deleteBtn = document.createElement("button");
deleteBtn.innerText = "Delete";
deleteBtn.addEventListener("click", function () {
taskList.removeChild(listItem);
});
listItem.appendChild(deleteBtn); // Add delete button to the list item
taskList.appendChild(listItem); // Add the list item to the task list
taskInput.value = ""; // Clear the input field
} else {
alert("Please enter a task!");
}
});
How It Works
- User types a task in the input field.
- Clicking "Add Task" creates a new
<li>element with the task.
- Each task has a "Delete" button to remove it.
6. Key Takeaways
DOM Access: Use methods likegetElementByIdandquerySelector.
DOM Modification: Change content, styles, and classes dynamically.
Event Handling: UseaddEventListenerto 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
mouseoverandkeydownin 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!
SOCIAL SHARE CARD GENERATOR