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15.4.2 Getting and Setting Non-HTML Attributes

15.4.2 Getting and Setting Non-HTML Attributes


As described above, HTMLElement and its subtypes define properties that correspond to the standard attributes of HTML elements. The Element type also defines getAttribute() and setAttribute() methods that you can use to query and set nonstandard HTML attributes and to query and set attributes on the elements of an XML document:

var image = document.images[0]; var width = parseInt(image.getAttribute("WIDTH")); image.setAttribute("class", "thumbnail");

The code above highlights two important differences between these methods and the property-based API described above. First, attribute values are all treated as strings. getAttribute() never returns a number, boolean, or object. Second, these methods use standard attribute names, even when those names are reserved words in JavaScript. For HTML elements, the attribute names are case insensitive.

Element also defines two related methods, hasAttribute() and removeAttribute(), which check for the presence of a named attribute and remove an attribute entirely. These methods are particularly useful with boolean attributes: these are attributes (such as the disabled attribute of HTML form elements) whose presence or absence from an element matters but whose value is not relevant.

If you are working with XML documents that include attributes from other namespaces, you can use the namespaced variants of these four methods: getAttributeNS(), setAttributeNS(), hasAttributeNS(), and removeAttributeNS(). Instead of taking a single attribute name string, these methods take two. The first is the URI that identifies the namespace. The second is usually the unqualified local name of the attribute within the namespace. For setAttributeNS() only, however, the second argument is the qualified name of the attribute and includes the namespace prefix. You can read more about these namespace-aware attribute methods in Part IV .

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