NodeList
Baseline
Widely available
This feature is well established and works across many devices and browser versions. It’s been available across browsers since July 2015.
NodeList objects are collections of nodes, usually returned by properties such as Node.childNodes and methods such as document.querySelectorAll().
This interface was an attempt to create an unmodifiable list and only continues to be supported to not break code that's already using it. Modern APIs represent list structures using types based on JavaScript arrays, thus making many array methods available, and at the same time imposing additional semantics on their usage (such as making their items read-only).
These historical reasons do not mean that you as a developer should avoid NodeList. You don't create NodeList objects yourself, but you get them from APIs such as Document.querySelectorAll(), and these APIs are not deprecated. However, be careful of the semantic differences from a real array.
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.
In most 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 childNodes = parent.childNodes;
console.log(childNodes.length); // let's assume "2"
parent.appendChild(document.createElement("div"));
console.log(childNodes.length); // outputs "3"
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 is the only API that 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.lengthRead only-
The number of nodes in the
NodeList.
Instance methods
NodeList.item()-
Returns an item in the list by its index, or
nullif the index is out-of-bounds.An alternative to accessing
nodeList[i](which instead returnsundefinedwheniis 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 from0and the values are nodes.) NodeList.forEach()-
Executes a provided function once per
NodeListelement, 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
iteratorallowing 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:
for (let i = 0; i < myNodeList.length; i++) {
let item = myNodeList[i];
}
Don't use for...in to enumerate the items in NodeLists, 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 over NodeList objects correctly:
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 # interface-nodelist |
Browser compatibility
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