NodeList

NodeList objects are collections of nodes such as those returned by properties such as Node.childNodes and the document.querySelectorAll() method.

In some cases, the NodeList is a live collection, which means that changes in the DOM are reflected in the collection. For example, Node.childNodes is live:

var parent = document.getElementById('parent');
var child_nodes = parent.childNodes;
console.log(child_nodes.length); // let's assume "2"
parent.appendChild(document.createElement('div'));
console.log(child_nodes.length); // should output "3"

In other cases, the NodeList is a static collection, meaning any subsequent change in the DOM does not affect the content of the collection. document.querySelectorAll() 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 how you cache the length of the list in particular.

Properties

NodeList.length

The number of nodes in the NodeList.

Methods

NodeList.item()

Returns an item in the list by its index, or null if the index is out-of-bounds; can be used as an alternative to simply accessing nodeList[idx] (which instead returns undefined when idx is out-of-bounds).

NodeList.entries()

Returns an iterator allowing to go through all key/value pairs contained in this object.

NodeList.forEach()

Executes a provided function once per NodeList element.

NodeList.keys()

Returns an iterator allowing to go through all keys of the key/value pairs contained in this object.

NodeList.values()

Returns an iterator allowing to go through all values of the key/value pairs contained in this object.

Example

It's possible to loop over the items in a NodeList using:

for (var i = 0; i < myNodeList.length; i++) {
  var item = myNodeList[i];  // Calling myNodeList.item(i) isn't necessary in JavaScript
}

Don't be tempted to use for...in or for each...in to enumerate the items in the list, since that will also enumerate the length and item properties of the NodeList 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:

var list = document.querySelectorAll( 'input[type=checkbox]' );
for (var item of list) {
  item.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.

var list = document.querySelectorAll( 'input[type=checkbox]' );
Array.prototype.forEach.call(list, function (item) {
  item.checked = true;
});

Specifications

Browser compatibility