Just Learn Code

Mastering HTML DOM: Understanding the NodeList Object

Introduction to HTML DOM

The HTML DOM (Document Object Model) provides a powerful interface for web developers to create dynamic and interactive web pages. It represents the page as a tree structure of nodes and objects that can be manipulated using JavaScript.

In this article, we’ll explore the fundamental concepts of HTML DOM that you need to understand to build great web applications.

Node Hierarchy in the DOM Tree Structure

In the HTML DOM, every element on a web page is an object. These objects are organized in a hierarchy representing the structure of the HTML document.

Nodes are the building blocks of the DOM tree structure. Each node has a parent, zero or more children, and zero or more sibling nodes.

The top-most node is the document object, which represents the entire HTML document. The DOM tree structure makes it easy to traverse and manipulate nodes on a web page.

For example, you can access the parent element of a given node, find the children of an element, or iterate over the sibling nodes of an element.

Difference between HTML Nodes and Elements

In the DOM, nodes are the basic building blocks, and elements are a specific type of nodes that represent the tags that define the structure and content of a web page. An element node represents the entire tag enclosing the content and any child nodes.

For example, the

tag creates a paragraph element node, while the text content inside the tag creates a text node.

JavaScript NodeList Object

The NodeList object is a collection of DOM nodes returned by a function or method. It is similar to an array, but with some critical differences.

Unlike an array, the NodeList is read-only, and you cannot perform array methods like push(), pop(), or sort() on it. However, you can access individual nodes using an index, just like an array.

Accessing Nodes in a NodeList Object

There are two main ways to access nodes in a NodeList object: by name and index. You can use the name of the node to select all the nodes with that tag name, like document.getElementsByTagName(‘p’).

This returns a NodeList object containing all the

element nodes on the page. Alternatively, you can access individual nodes using an index, like document.getElementsByTagName(‘p’)[0].

This returns the first

element node on the page.

Difference between NodeList and HTMLCollection Objects and their Access Methods

HTMLCollection is another collection of DOM Nodes, but it’s specific to a particular document object. For example, you can access the forms on a web page using document.forms, which returns an HTMLCollection object.

The key difference between NodeList and HTMLCollection is that NodeList is dynamic, while HTMLCollection is static. The HTMLCollection object is updated only when the DOM tree structure changes dynamically.

On the other hand, the NodeList object updates live as you modify the DOM tree.

Types of Nodes that can be held in a NodeList Object

A NodeList object can contain different types of nodes, including element nodes, attribute nodes, text nodes, and comment nodes. Element nodes represent the HTML tags that define the structure and content of a web page.

Attribute nodes represent the attributes of an element, while text nodes hold the actual text content inside an HTML tag. Comment nodes hold the comments written in HTML source code, and they don’t get rendered on the page.

Conclusion

Understanding the fundamental concepts of HTML DOM is essential for any web developer. By mastering the basic concept of the DOM tree structure and the different types of nodes that can be held in a NodeList object, developers can create dynamic and interactive web applications, making it easier for users to interact with a web page.

The interface provided by the HTML DOM makes it easy to manipulate and traverse nodes, making it easy to create dynamic web pages.

3) Static vs

Live NodeList Objects

In the previous section, we talked about the NodeList object, which is a collection of DOM nodes. NodeList objects can be either live or static.

A live NodeList is automatically updated when the DOM tree structure is modified programmatically, while static node lists are not updated. Let’s take a closer look at the difference between live and static node lists.

Live NodeList Objects

A live NodeList is updated automatically when the DOM tree structure changes. This means that any changes made to the DOM will immediately be reflected in the NodeList object.

For example, suppose we have a div element with three child elements (two paragraphs and one image). If we retrieve the childNodes of that div element and log the length of the resulting NodeList object to the console, we will see a length of 3.

Now, let’s append another child element to the div, like a span element. If we log the length of the NodeList again, we’ll see that the length has increased to 4.

This is because we’re working with a live NodeList, and any modifications to the DOM tree are immediately updated in the NodeList. To see this in action, we can open a browser console and run the following code:

“`

const div = document.querySelector(‘div’);

const childNodes = div.childNodes;

console.log(childNodes.length); // Outputs 3

div.appendChild(document.createElement(‘span’));

console.log(childNodes.length); // Outputs 4

“`

Static NodeList Objects

In contrast, a static NodeList is not updated automatically when the DOM tree is modified. A static NodeList is created when a query is made for a list of nodes, and it never receives any updates, even if the DOM tree is modified.

One example of a method that returns a static NodeList is document.querySelectorAll(). This method allows you to retrieve a list of nodes that match a CSS selector.

The result is a static NodeList that contains all the matched nodes at the time the query was run. For example, suppose we have the following HTML code:

“`

Static NodeList Example

Paragraph 1

Paragraph 2

An image

“`

If we retrieve all the elements matching the ‘p’ tag using document.querySelectorAll(‘p’), we will get a static NodeList containing two nodes.

If later, we add another p element to the div, the NodeList will not be updated. To see this in action, we can run the following code in the browser console:

“`

const paragraphs = document.querySelectorAll(‘p’);

console.log(paragraphs.length); // Outputs 2

document.querySelector(‘div’).appendChild(document.createElement(‘p’));

console.log(paragraphs.length); // Outputs 2

“`

In this example, we’ve retrieved the paragraphs using document.querySelectorAll(‘p’).

After that, we append another paragraph element to the div. However, when we log the length of the NodeList object, we still get two paragraphs.

This is because the NodeList is static and is not automatically updated when the DOM tree is modified.

4) Operations on NodeList Object

Now that we know how to work with NodeList objects let’s look at some of the common operations we need to carry out on a NodeList object.

Looping and Index Access

A NodeList object can be accessed using an index like an array, using the square bracket notation []. The first index is 0, and we can loop through the entire NodeList using a for loop.

Here’s an example:

“`

const nodes = document.querySelectorAll(‘p’);

for (let i = 0; i < nodes.length; i++) {

console.log(nodes[i]);

}

“`

In this example, we’re getting all the paragraph nodes on a web page using document.querySelectorAll(‘p’). We loop through the entire NodeList using a for loop that runs from 0 to less than the length of the NodeList.

The loop will print each element of the NodeList to the console.

Lack of Array Operations in a NodeList Object

Unlike an array, the NodeList object lacks some common array operations like pop(), push(), join(), etc. For example, we cannot remove the last element of a NodeList by calling pop() or append an element to the NodeList by calling push().

If we attempt to use these array operations on a NodeList object, we will receive an error. Conversion of NodeList to JavaScript Array using Array.from() Method

Fortunately, we can easily convert a NodeList object to a regular JavaScript array if we need to perform array operations on it.

We can use the Array.from() method to convert a NodeList into an array. Here’s an example:

“`

const nodes = document.querySelectorAll(‘p’);

const nodesArray = Array.from(nodes);

nodesArray.pop();

nodesArray.push(document.createElement(‘p’));

console.log(nodesArray.join(‘, ‘));

“`

In this example, we first convert the NodeList object that contains all the paragraph elements on the page to an array using the Array.from() method.

Now we can use all the array methods like pop() or push() on the newly created array. We also log the entire array as a string using the join() method.

Conclusion

In summary, a NodeList object is a collection of DOM nodes that are organized in a hierarchical tree structure. We can work with a NodeList object using an index or loop through it to access each node.

We have seen both live and static node lists and how to differentiate between them. Finally, we can convert a NodeList object to a JavaScript array to use all the array operations available in JavaScript.

Understanding these concepts is essential when working with the HTML DOM to create dynamic and interactive web applications. In conclusion, understanding the concepts of HTML DOM and the properties and methods provided by the NodeList object is essential for web developers who want to create dynamic and interactive web pages.

We have seen the differences between live and static node lists, how to loop through a NodeList object, and how to convert it to a JavaScript array to use array operations. Further, understanding this topic will provide developers with the necessary skills to create compelling user interfaces and user experiences on the web.

By mastering these concepts, web developers can write more efficient and cleaner code to deliver better performance and functionality.

Popular Posts