NodeList
objects are collections of nodes, usually returned by properties such as Node.childNodes
and methods such as document.querySelectorAll()
.
Note: Although NodeList
is not an Array
, it is possible to iterate over it with forEach()
. It can also be converted to a real Array
using Array.from()
.
However, some older browsers have not implemented NodeList.forEach()
nor Array.from()
. This can be circumvented by using Array.prototype.forEach()
— see this document's Example.
Although they are both considered NodeList
s, there are 2 varieties of NodeList: live and static.
In some cases, the NodeList
is live, which means that changes in the DOM automatically update the collection.
For example, Node.childNodes
is live:
const parent = document.getElementById('parent');
let child_nodes = parent.childNodes;
console.log(child_nodes.length);
parent.appendChild(document.createElement('div'));
console.log(child_nodes.length);
In other cases, the NodeList
is static, where any changes in the DOM does not affect the content of the collection. The ubiquitous document.querySelectorAll()
method returns a static NodeList
.
It's good to keep this distinction in mind when you choose how to iterate over the items in the NodeList
, and whether you should cache the list's length
.
It's possible to loop over the items in a NodeList
using a for loop:
for (let i = 0; i < myNodeList.length; i++) {
let item = myNodeList[i];
}
Don't use for...in
to enumerate the items in NodeList
s, since they will also enumerate its length
and item
properties and cause errors if your script assumes it only has to deal with element
objects. Also, for..in
is not guaranteed to visit the properties in any particular order.
for...of
loops will loop over NodeList
objects correctly:
const list = document.querySelectorAll('input[type=checkbox]');
for (let checkbox of list) {
checkbox.checked = true;
}
Recent browsers also support iterator methods (forEach()
) as well as entries()
, values()
, and keys()
.
There is also an Internet Explorer-compatible way to use Array.prototype.forEach
for iteration:
const list = document.querySelectorAll('input[type=checkbox]');
Array.prototype.forEach.call(list, function (checkbox) {
checkbox.checked = true;
});