dltypeof - Custom JS typeof operator - DHTML Lab | 3

DOM Objects

dltypeof() will identify the two most often used types of DOM objects: elements and collections.

DOM Elements

DOM elements ( HTML tags ) have a type of "domelement".

DOM text nodes have a type of "textnode".

IE for Windows also supports the TextRange object. It can be neither created nor referred to in any other browser, but it has a type of "textrange" in IE-only applications.

DOM Collections

dltypeof() will return "domcollection" for all collections whether they are represented by properties like anchors or by methods that return collections like getElementsByTagName().

dltypeof() also handles browser-specific collections. Some, like all, can be referenced in cross-browser applications, often for browser-identification. These collections have a type of "undefined" if they are not supported.
Other browser-specific collections, like text rectangle, cannot be referenced in cross-browser applications, as they are created by unsupported methods.

In general, dltypeof() will handle return values correctly for the environment it resides in, whether it is a cross-browser script or a browser-specific script.

The window and window.frames Problem

The window object and the window.frames collection are identified as the same object in both Netscape and IE. That is, not as objects of similar types but the same object, with the same property values and methods and they are interchangeable in use. This, of course, makes no sense (at least not to me), and it could be a holdover from the original JavaScript implementation.

It is therefore not possible to differentiate between the two and identify window as a special object type ( "window" ) and window.frames as a collection of type "domcollection".

This problem does not exist in Opera, where window and window.frames are separate objects of different types.

However, dltypeof() cannot return different values for the same object in different browsers if the object is supported in all browsers. So, both window and window.frames have a type of "window" in all browsers.

The following table lists all the possible return values for DOM objects as well as the original typeof() return values

DOM object	typeof() return value	dltypeof() return value
HTML element ( DIV, IMG, P, TABLE, etc. )	object	domelement
text node	object	textnode
text range	object	textrange	n/a
Standard collections ( anchors, applets, areas, attributes, cells, childNodes, elements, embeds, forms, images, links, options, rows, tbodies, etc. )	object	domcollection
IE collections - supported by Opera ( all, children, scripts, tags, etc. )	object	domcollection		undefined
IE collections - IE only ( behavioururns, filters, document.frames, namespaces, etc. )	object	domcollection	undefined
IE collections - IE only - IE-specific applications ( control range, imports, pages, rules, text rectangle, etc. )	object	domcollection	n/a
Non-IE collections ( mimeTypes, plugins )	object	object	mimetypecollection plugincollection
IE and NS collections ( styleSheets )	object	domcollection	undefined	domcollection
frames	object	window
window	object	window

The dltypeof() function is listed on the final page.