NodeList
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()
.
Live vs. Static NodeLists
Although they are both considered NodeList
objects, there are 2 varieties of NodeList: live and static.
Live NodeLists
In some cases, the NodeList
is live, which means that changes in the DOM automatically update the collection.
For example, Node.childNodes
is live:
js
const parent = document.getElementById("parent");
let childNodes = parent.childNodes;
console.log(childNodes.length); // let's assume "2"
parent.appendChild(document.createElement("div"));
console.log(childNodes.length); // outputs "3"
Static NodeLists
In other cases, the NodeList
is static, where any changes in the DOM do 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
.
Instance properties
NodeList.length
-
The number of nodes in the
NodeList
.
Instance methods
NodeList.item()
-
Returns an item in the list by its index, or
null
if the index is out-of-bounds.An alternative to accessing
nodeList[i]
(which instead returnsundefined
wheni
is out-of-bounds). This is mostly useful for non-JavaScript DOM implementations. NodeList.entries()
-
Returns an
iterator
, allowing code to go through all key/value pairs contained in the collection. (In this case, the keys are integers starting from0
and the values are nodes.) NodeList.forEach()
-
Executes a provided function once per
NodeList
element, passing the element as an argument to the function. NodeList.keys()
-
Returns an
iterator
, allowing code to go through all the keys of the key/value pairs contained in the collection. (In this case, the keys are integers starting from0
.) NodeList.values()
-
Returns an
iterator
allowing code to go through all values (nodes) of the key/value pairs contained in the collection.
Example
It's possible to loop over the items in a NodeList
using a for loop:
js
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 loop over NodeList
objects correctly:
js
const list = document.querySelectorAll("input[type=checkbox]");
for (const checkbox of list) {
checkbox.checked = true;
}
Browsers also support the iterator method (forEach()
) as well as entries()
, values()
, and keys()
.
Specifications
Specification |
---|
DOM Standard # interface-nodelist |
Browser compatibility
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