HTMLCollection
The HTMLCollection
interface represents a generic collection (array-like object similar to arguments
) of elements (in document order) and offers methods and properties for selecting from the list.
Note: This interface is called HTMLCollection
for historical reasons (before the modern DOM, collections implementing this interface could only have HTML elements as their items).
An HTMLCollection
in the HTML DOM is live; it is automatically updated when the underlying document is changed. For this reason it is a good idea to make a copy (e.g., using Array.from
) to iterate over if adding, moving, or removing nodes.
Note: 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 use types that wrap around ECMAScript array types instead, so you can treat them like ECMAScript arrays, and at the same time impose additional semantics on their usage (such as making their items read-only).
Instance properties
HTMLCollection.length
Read only-
Returns the number of items in the collection.
Instance methods
HTMLCollection.item()
-
Returns the specific node at the given zero-based
index
into the list. Returnsnull
if theindex
is out of range.An alternative to accessing
collection[i]
(which instead returnsundefined
wheni
is out-of-bounds). This is mostly useful for non-JavaScript DOM implementations. HTMLCollection.namedItem()
-
Returns the specific node whose ID or, as a fallback, name matches the string specified by
name
. Matching by name is only done as a last resort, only in HTML, and only if the referenced element supports thename
attribute. Returnsnull
if no node exists by the given name.An alternative to accessing
collection[name]
(which instead returnsundefined
whenname
does not exist). This is mostly useful for non-JavaScript DOM implementations.
Usage in JavaScript
HTMLCollection
also exposes its members directly as properties by both name and index. HTML IDs may contain :
and .
as valid characters, which would necessitate using bracket notation for property access. Currently HTMLCollections
does not recognize purely numeric IDs, which would cause conflict with the array-style access, though HTML5 does permit these.
For example, assuming there is one <form>
element in the document and its id
is myForm
:
js
let elem1, elem2;
// document.forms is an HTMLCollection
elem1 = document.forms[0];
elem2 = document.forms.item(0);
alert(elem1 === elem2); // shows: "true"
elem1 = document.forms.myForm;
elem2 = document.forms.namedItem("myForm");
alert(elem1 === elem2); // shows: "true"
elem1 = document.forms["named.item.with.periods"];
Specifications
Specification |
---|
DOM Standard # interface-htmlcollection |
Browser compatibility
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