HTMLCollection - Web APIs 编辑

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.

Properties

HTMLCollection.length Read only

Returns the number of items in the collection.

Methods

HTMLCollection.item()

Returns the specific node at the given zero-based index into the list. Returns null if the index is out of range.

An alternative to accessing collection[i] (which instead returns  undefined when i 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 the name attribute. Returns null if no node exists by the given name.

An alternative to accessing collection[name] (which instead returns undefined when name 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:

var 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	Status	Comment
DOM The definition of 'HTMLCollection' in that specification.	Living Standard

Browser compatibility

BCD tables only load in the browser

See also

• NodeList
• HTMLFormControlsCollection, HTMLOptionsCollection