02. Retrieving a single element and DOM traversal

When selecting elements from the DOM, we can either select one or many nodes. Let's start with retrieving a single element.

To retrieve an element, we use DOM queries. These are the methods used through JavaScript that we can use to find elements on the DOM tree. Oftentimes, the elements we select are stored into a variable, which serves as a reference to the node; this is known as caching.

getElementById

The most efficient way to obtain an element is through its id attribute. We may do this with the getElementById() method, in which we simply pass in the name of the id. Since we know that no two elements can share the same id, we are ensured that the browser terminates right after finding the first id, resulting in quickness and responsivity.

var firstItem = document.getElementById('first')

This command will store the reference to the element with an id of first within the firstItemvariable.

querySelector

Another way to select just one element is through a query selector. Given a CSS selector, this returns only the first matched item.

firstParagraph = document.querySelector('p') # First 

tag. document.querySelector('.item') # First element with a class "item"

Traversing the DOM - single elements

Once we have selected a single element, we may access the nodes around it through these properties:

parent
Select parent of current node.
previousSibling
Select the previous sibling node.
nextSibling
Select the next sibling node.
firstChild
Select the first child of current element.
lastChild
Select last child of current element.

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