HTMLCollection

HTMLCollection 介面表示了一種成員為 Element 物件的通用集合（如 arguments 一般的類陣列，成員順序同元素在文件中的順序），並提供了可用來選取集合成員的方法與屬性。

備註： This interface is called HTMLCollection for historical reasons (before DOM4, collections implementing this interface could only have HTML elements as their items).

HTMLCollection 物件對 HTML DOM 而言具有即時性（live），如果底層的文件（document 物件）發生改變，HTMLCollection 物件會自動更新至最新的狀態。

屬性

HTMLCollection.length (en-US) Read only

Returns the number of items in the collection.

方法

HTMLCollection.item() (en-US)

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

HTMLCollection.namedItem() (en-US)

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.

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"];

瀏覽器相容性

Different browsers behave differently when there are more than one elements matching the string used as an index (or namedItem's argument). Firefox 8 behaves as specified in DOM 2 and DOM4, returning the first matching element. WebKit browsers and Internet Explorer in this case return another HTMLCollection and Opera returns a NodeList of all matching elements.

規範

Specification
DOM Standard
# interface-htmlcollection

參見