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June 10, 2023

JavaScript: Enhancing the DOM - A Comprehensive Guide to Manipulating HTML Elements with JavaScript

Lynda.com - JavaScript Enhancing the DOM

If you want to learn how to use JavaScript to create dynamic and interactive web pages, you need to understand how it connects to and controls the Document Object Model (DOM). The DOM is a representation of every HTML element on a web page as a node in a tree-like structure. By manipulating the DOM with JavaScript, you can create, modify, delete, and edit existing page content.

Lynda.com - JavaScript Enhancing the 11

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In this article, we will review a course from Lynda.com that teaches you how to enhance the DOM with JavaScript. The course is called JavaScript: Enhancing the DOM and it is taught by Ray Villalobos, a senior staff instructor at LinkedIn Learning. Ray Villalobos has over 20 years of experience in web development and design, and he specializes in JavaScript frameworks, tooling, GitHub, full stack development, and web design.

The course covers topics such as:

What is the DOM and why is it important?

How to access and manipulate the DOM with JavaScript

How to build a project that enhances the DOM with JavaScript

The course is suitable for intermediate-level developers who have some basic knowledge of HTML, CSS, and JavaScript. It takes about 2 hours to complete and it includes transcripts, exercise files, quizzes, and a certificate of completion. You can access the course online on Lynda.com or LinkedIn Learning with a free trial or a subscription.

What is the DOM and why is it important?

The Document Object Model (DOM) is a programming interface that allows you to access and manipulate HTML documents as objects. Each HTML element on a web page is represented by a node in a tree-like structure called the DOM tree. The nodes have properties (such as attributes) and methods (such as appendChild) that you can use to change their characteristics or behavior.

The DOM is important because it provides a way for JavaScript to interact with HTML elements dynamically. For example, you can use JavaScript to:

Select an element by its ID or class name

Change its text content or HTML content

Add or remove an attribute or a style

Create a new element and insert it into the DOM tree

Remove an existing element from the DOM tree

Attach an event listener to an element to handle user actions

By manipulating the DOM with JavaScript, you can create web pages that respond to user input, display dynamic content, animate elements, validate forms, and more.

How to access and manipulate the DOM with JavaScript

In order to access and manipulate the DOM with JavaScript, you need to use some methods and properties that are available on the global window object or the document object. The window object represents the browser window that contains the web page, while the document object represents the HTML document itself.

Some of the most common methods and properties that you can use to interact with the DOM are:

Selecting elements by ID, class, tag name, and query selector

To select an element by its ID, you can use the getElementById method on the document object. For example, if you have an element with an ID of "title", you can select it with this code:

var title = document.getElementById("title");

To select multiple elements by their class name, you can use the getElementsByClassName method on the document object or any other element. For example, if you have several elements with a class of "item", you can select them with this code:

var items = document.getElementsByClassName("item");

To select multiple elements by their tag name, you can use the getElementsByTagName method on the document object or any other element. For example, if you have several <li> elements, you can select them with this code:

var listItems = document.getElementsByTagName("li");

To select one or more elements by using a CSS selector, you can use the querySelector or querySelectorAll method on the document object or any other element. For example, if you want to select the first element that matches the selector "#title .item", you can use this code:

var firstItem = document.querySelector("#title .item");

If you want to select all the elements that match the selector "#title .item", you can use this code:

var allItems = document.querySelectorAll("#title .item");

Modifying attributes and styles of DOM elements

To modify an attribute of a DOM element, such as its ID, class, href, src, or data-*, you can use the setAttribute, getAttribute, or removeAttribute method on the element. For example, if you want to change the ID of an element to "new-id", you can use this code:

element.setAttribute("id", "new-id");

If you want to get the value of an attribute of an element, such as its ID, class, href, src, or data-*, you can use the getAttribute method on the element. For example, if you want to get the value of the href attribute of an element, you can use this code:

var href = element.getAttribute("href");

If you want to remove an attribute from an element, such as its ID, class, href, src, or data-*, you can use the removeAttribute method on the element. For example, if you want to remove the class attribute from an element, you can use this code:

element.removeAttribute("class");

To modify a style of a DOM element, such as its color, font-size, display, or margin, you can use the style

property on the element. The style

property is an object that contains all the CSS properties that apply to the element. You can access and change any property by using dot notation or bracket notation. For example, if you want to change the color of an element to red, you can use this code:

element.style.color = "red"; // or Creating, appending, cloning, replacing, and removing DOM nodes

To create a new DOM node, such as an element, a text node, or a comment node, you can use the createElement, createTextNode, or createComment method on the document object. For example, if you want to create a new <div> element, you can use this code:

var div = document.createElement("div");

If you want to create a new text node with the content "Hello world", you can use this code:

var text = document.createTextNode("Hello world");

If you want to create a new comment node with the content "This is a comment", you can use this code:

var comment = document.createComment("This is a comment");

To append a DOM node to another DOM node as its last child, you can use the appendChild method on the parent node. For example, if you want to append the text node to the div element, you can use this code:

div.appendChild(text);

To clone a DOM node and optionally its children, you can use the cloneNode method on the node. The method takes a boolean argument that indicates whether to clone the children or not. For example, if you want to clone the div element and its children, you can use this code:

var clone = div.cloneNode(true);

To replace a DOM node with another DOM node in the same position in the DOM tree, you can use the replaceChild method on the parent node. The method takes two arguments: the new node and the old node. For example, if you want to replace the div element with the clone element, you can use this code:

div.parentNode.replaceChild(clone, div);

To remove a DOM node from its parent node in the DOM tree, you can use the removeChild method on the parent node. The method takes one argument: the node to be removed. For example, if you want to remove the clone element from its parent node, you can use this code:

clone.parentNode.removeChild(clone);

To insert a DOM node before another DOM node as its sibling in the DOM tree, you can use the insertBefore method on the parent node. The method takes two arguments: the new node and the reference node. For example, if you want to insert the clone element before the div element, you can use this code:

How to build a project that enhances the DOM with JavaScript

In this section, we will learn how to build a project that enhances the DOM with JavaScript. The project is a pop-up overlay that displays a centered image when the user clicks on a thumbnail. The pop-up overlay also has a close button and a caption for the image. The project will use JavaScript to create and manipulate the DOM elements, as well as to handle events such as click, scroll, and resize.

The project consists of three main steps:

Creating the HTML structure and CSS styles for the pop-up overlay

Writing the JavaScript code to handle events and display the pop-up overlay

Testing and debugging the project with developer tools

Creating the HTML structure and CSS styles for the pop-up overlay

The first step is to create the HTML structure and CSS styles for the pop-up overlay. The HTML structure consists of a <div> element with an ID of "overlay" that contains three child elements: a <span> element with an ID of "close" that acts as the close button, an <img> element with an ID of "image" that displays the image, and a <p> element with an ID of "caption" that shows the caption for the image. The HTML structure looks like this:

The CSS styles consist of some rules that position and style the overlay and its components. The CSS styles look like this:

#overlay position: fixed; top: 0; left: 0; width: 100%; height: 100%; background-color: rgba(0,0,0,0.8); display: none; #close position: absolute; top: 10px; right: 10px; color: white; font-size: 30px; cursor: pointer; #image position: absolute; top: 50%; left: 50%; transform: translate(-50%, -50%); max-width: 80%; max-height: 80%; #caption position: absolute; bottom: 10px; left: 10px; color: white;

Writing the JavaScript code to handle events and display the pop-up overlay

The second step is to write the JavaScript code to handle events and display the pop-up overlay. The JavaScript code consists of some variables that store references to the DOM elements, some functions that perform tasks such as showing or hiding the overlay, setting the image source and caption, and centering the image, and some event listeners that trigger those functions when certain events occur.

The JavaScript code looks like this:

// Get references to DOM elements var overlay = document.getElementById("overlay"); var close = document.getElementById("close"); var image = document.getElementById("image"); var caption = document.getElementById("caption"); // Show overlay function function showOverlay(src, alt)

image.src = src; image.alt = alt; // Set caption text caption.textContent = alt; // Show overlay overlay.style.display = "block"; // Center image centerImage(); // Hide overlay function function hideOverlay() // Hide overlay overlay.style.display = "none"; // Center image function function centerImage() // Get image dimensions var imageWidth = image.offsetWidth; var imageHeight = image.offsetHeight; // Get window dimensions var windowWidth = window.innerWidth; var windowHeight = window.innerHeight; // Calculate image position var imageTop = (windowHeight - imageHeight) / 2; var imageLeft = (windowWidth - imageWidth) / 2; // Set image position image.style.top = imageTop + "px"; image.style.left = imageLeft + "px"; // Add event listener to close button close.addEventListener("click", hideOverlay); // Add event listener to window for scroll and resize events window.addEventListener("scroll", hideOverlay); window.addEventListener("resize", centerImage); // Add event listener to document for click events on thumbnails document.addEventListener("click", function(event) // Get the element that was clicked var target = event.target; // Check if the element is a thumbnail if (target.classList.contains("thumbnail")) // Get the image source and alt attribute from the thumbnail var src = target.src; var alt = target.alt; // Show overlay with the image source and alt attribute showOverlay(src, alt); // Prevent default behavior of the click event event.preventDefault(); );

Testing and debugging the project with developer tools

The third step is to test and debug the project with developer tools. Developer tools are a set of tools that are built into most modern browsers that allow you to inspect and modify the DOM, run JavaScript commands, and fix errors. You can access the developer tools by pressing F12 or Ctrl+Shift+I on your keyboard, or by right-clicking on any element on the web page and selecting Inspect.

Some of the features of the developer tools that are useful for this project are:

The Elements panel, which shows the DOM tree and allows you to edit the HTML elements and CSS styles

The Console panel, which shows the JavaScript output and errors and allows you to run JavaScript commands

The Sources panel, which shows the JavaScript files and allows you to set breakpoints and step through the code

The Network panel, which shows the requests and responses for the web page resources

By using the developer tools, you can test if the project works as expected, and if not, you can debug it by finding and fixing any errors in the code.

Conclusion

In this article, we have reviewed a course from Lynda.com that teaches you how to enhance the DOM with JavaScript. The course is called JavaScript: Enhancing the DOM and it is taught by Ray Villalobos, a senior staff instructor at LinkedIn Learning.

We have learned about:

What is the DOM and why is it important?

How to access and manipulate the DOM with JavaScript

How to build a project that enhances the DOM with JavaScript

If you want to learn more about JavaScript and the DOM, you can check out some of these resources:

Introduction to the DOM - MDN Web Docs

HTML DOM - W3Schools

DOM nodes - The Modern JavaScript Tutorial

The Document Object Model - Eloquent JavaScript

FAQs

Here are some frequently asked questions about JavaScript and the DOM:

What is the difference between the DOM and the HTML?

The HTML is the markup language that defines the structure and content of a web page. The DOM is a programming interface that represents the HTML elements as objects in a tree-like structure. The DOM allows you to access and manipulate the HTML elements with JavaScript.

What is the difference between the DOM and jQuery?

jQuery is a JavaScript library that simplifies the process of accessing and manipulating the DOM with JavaScript. jQuery provides a set of methods and selectors that make it easier to find, modify, create, and animate DOM elements. jQuery also handles cross-browser compatibility issues and provides some additional features such as AJAX and plugins.

How can I check if a DOM element exists?

You can check if a DOM element exists by using one of the methods that select an element, such as getElementById, querySelector, or querySelectorAll, and then checking if the returned value is not null or not empty. For example, you can use this code to check if an element with an ID of "title" exists:

var title = document.getElementById("title"); if (title) // The element exists else // The element does not exist

How can I add an event listener to multiple elements?

You can add an event listener to multiple elements by using one of the methods that select multiple elements, such as getElementsByClassName, getElementsByTagName, or querySelectorAll, and then looping through the returned collection and calling the addEventListener method on each element. For example, you can use this code to add a click event listener to all elements with a class of "thumbnail":

var thumbnails = document.getElementsByClassName("thumbnail"); for (var i = 0; i

How can I remove an event listener from an element?

You can remove an event listener from an element by using the removeEventListener method on the element. The method takes the same arguments as the addEventListener method: the event type, the event handler function, and optionally, a boolean value that indicates whether to use capturing or bubbling. You need to pass the same arguments that you used when you added the event listener. For example, you can use this code to remove a click event listener from an element with an ID of "close":

var close = document.getElementById("close"); close.removeEventListener("click", hideOverlay); 71b2f0854b

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