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JavaScript HTML DOM Node Lists


The HTML DOM NodeList Object
A NodeList object is a list (collection) of nodes extracted from a
document.
A NodeList object is almost the same as an HTMLCollection object.
Some (older) browsers return a NodeList object instead of an HTMLCollection
for methods like getElementsByClassName().
All browsers return a NodeList object for the property childNodes. 
Most browsers return a NodeList object for the method querySelectorAll().
The following code selects all <p> nodes in a document:

Example

const myNodeList = document.querySelectorAll("p");

The elements in the NodeList can be accessed by an index number.
To access the
second <p> node you can write:

myNodeList[1]

Try it Yourself »

Note: The index starts at 0.

HTML DOM Node List Length
The length property defines the number of nodes in a node list:

Example

myNodelist.length

Try it Yourself »

The length property is useful when you want to loop through the nodes in a node
list:

Example
Change the color of all <p> elements in a node
list:

const myNodelist = document.querySelectorAll("p");
for (let i = 0; i < myNodelist.length; i++) {
  myNodelist.style.color = "red";
}

Try it Yourself »








The Difference Between an HTMLCollection and a NodeList
A NodeList and an HTMLcollection is very much the same thing.
Both are array-like collections (lists) of nodes (elements) extracted from a
document. The nodes can be accessed by index numbers. The index starts at 0.
Both have a length property that returns the number of elements in the list (collection).
An HTMLCollection is a collection of document elements.
A NodeList is a collection of document nodes (element nodes, attribute nodes, and text nodes).
HTMLCollection items can be accessed by their name, id, or index number.
NodeList items can only be accessed by their index number.
An HTMLCollection is always a live collection. Example: If you add a <li> element to a list in the DOM, the list in the HTMLCollection will also change.
A NodeList is most often a static collection. Example: If you add a <li> element to a list in the DOM, the list in NodeList will not change.
The getElementsByClassName() and getElementsByTagName()
methods return a live HTMLCollection.
The querySelectorAll() method returns a static NodeList.
The childNodes property returns a live NodeList.


Not an Array!
A NodeList may look like an array, but it is not.
You can loop through a NodeList and refer to its nodes by index.
But, you cannot use Array methods like push(), pop(), or join() on a NodeList.













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Reference: https://www.w3schools.com/js/js_htmldom_nodelist.asp