How To Make Changes to the DOM
In the previous two installments of the Understanding the DOM series, we learned How To Access Elements in the DOM and How To Traverse the DOM. Using this knowledge, a developer can use classes, tags, ids, and selectors to find any node in the DOM, and use parent, child, and sibling properties to find relative nodes.
In this tutorial, we will go over how to create new nodes and insert them into the DOM, replace existing nodes, and remove nodes.
Creating New Nodes
In a static website, elements are added to the page by directly writing HTML in an
createTextNode() methods are used to create new nodes in the DOM.
||Create a new element node|
||Create a new text node|
||Get or set the text content of an element node|
||Get or set the HTML content of an element|
To begin, let’s create an
index.html file and save it in a new project directory.
<!DOCTYPE html> <html lang="en"> <head> <title>Learning the DOM</title> </head> <body> <h1>Document Object Model</h1> </body> </html>
Right click anywhere on the page and select “Inspect” to open up Developer Tools, then navigate to the Console.
We will use
createElement() on the
document object to create a new
- const paragraph = document.createElement('p');
We’ve created a new
p element, which we can test out in the Console.
paragraph variable outputs an empty
p element, which is not very useful without any text. In order to add text to the element, we’ll set the
- paragraph.textContent = "I'm a brand new paragraph.";
Output<p>I'm a brand new paragraph.</p>
A combination of
textContent creates a complete element node.
An alternate method of setting the content of the element is with the
innerHTML property, which allows you to add HTML as well as text to an element.
- paragraph.innerHTML = "I'm a paragraph with <strong>bold</strong> text.";
While this will work and is a common method of adding content to an element, there is a possible cross-site scripting (XSS) risk associated with using the
textContent instead, which will strip out HTML tags.
It is also possible to create a text node with the
- const text = document.createTextNode("I'm a new text node.");
Output"I'm a new text node."
With these methods, we’ve created new elements and text nodes, but they are not visible on the front end of a website until they’ve been inserted into the document.
Inserting Nodes into the DOM
In order to see the new text nodes and elements we create on the front end, we will need to insert them into the
document. The methods
insertBefore() are used to add items to the beginning, middle, or end of a parent element, and
replaceChild() is used to replace an old node with a new node.
||Add a node as the last child of a parent element|
||Insert a node into the parent element before a specified sibling node|
||Replace an existing node with a new node|
To practice these methods, let’s create a to-do list in HTML:
<ul> <li>Buy groceries</li> <li>Feed the cat</li> <li>Do laundry</li> </ul>
When you load your page in the browser, it will look like this:
In order to add a new item to the end of the to-do list, we have to create the element and add text to it first, as we did in the “Creating New Nodes” section above.
- // To-do list ul element
- const todoList = document.querySelector('ul');
- // Create new to-do
- const newTodo = document.createElement('li');
- newTodo.textContent = 'Do homework';
Now that we have a complete element for our new to-do, we can add it to the end of the list with
- // Add new todo to the end of the list
You can see the new
li element has been appended to the end of the
<ul> <li>Buy groceries</li> <li>Feed the cat</li> <li>Do laundry</li> <li>Do homework</li> </ul>
Maybe we have a higher priority task to do, and we want to add it to the beginning of the list. We’ll have to create another element, as
createElement() only creates one element and cannot be reused.
- // Create new to-do
- const anotherTodo = document.createElement('li');
- anotherTodo.textContent = 'Pay bills';
We can add it to the beginning of the list using
insertBefore(). This method takes two arguments — the first is the new child node to be added, and the second is the sibling node that will immediately follow the new node. In other words, you’re inserting the new node before the next sibling node. This will look similar to the following pseudocode:
For our to-do list example, we’ll add the new
anotherTodo element before the first element child of the list, which is currently the
Buy groceries list item.
- // Add new to-do to the beginning of the list
- todoList.insertBefore(anotherTodo, todoList.firstElementChild);
<ul> <li>Pay bills</li> <li>Buy groceries</li> <li>Feed the cat</li> <li>Do laundry</li> <li>Do homework</li> </ul>
The new node has successfully been added at the beginning of the list. Now we know how to add a node to a parent element. The next thing we may want to do is replace an existing node with a new node.
We’ll modify an existing to-do to demonstrate how to replace a node. The first step of creating a new element remains the same.
- const modifiedTodo = document.createElement('li');
- modifiedTodo.textContent = 'Feed the dog';
replaceChild() takes two arguments — the new node, and the node to be replaced, as shown in the pseudocode below.
We will replace the third element child of the list with the modified to-do.
- // Replace existing to-do with modified to-do
- todoList.replaceChild(modifiedTodo, todoList.children);
<ul> <li>Pay bills</li> <li>Buy groceries</li> <li>Feed the dog</li> <li>Do laundry</li> <li>Do homework</li> </ul>
With a combination of
replaceChild(), you can insert nodes and elements anywhere in the DOM.
Removing Nodes from the DOM
Now we know how to create elements, add them to the DOM, and modify existing elements. The final step is to learn to remove existing nodes from the DOM. Child nodes can be removed from a parent with
removeChild(), and a node itself can be removed with
||Remove child node|
Using the to-do example above, we’ll want to delete items after they’ve been completed. If you completed your homework, you can remove the
Do homework item, which happens to be the last child of the list, with
<ul> <li>Pay bills</li> <li>Buy groceries</li> <li>Feed the dog</li> <li>Do laundry</li> </ul>
Another method could be to remove the node itself, using the
remove() method directly on the node.
- // Remove second element child from todoList
<ul> <li>Pay bills</li> <li>Feed the dog</li> <li>Do laundry</li> </ul>
remove(), you can remove any node from the DOM. Another method you may see for removing child elements from the DOM is setting the
innerHTML property of a parent element to an empty string (
""). This is not the preferred method because it is less explicit, but you might see it in existing code.