Inferring node placement via special sourceIndex values

I needed to know whether a node was in the DOM. Figuring there was a native property or method towards this end, I scoured Mozilla's documentation but could find nothing. Then Microsoft (yes, them) offered hope with Internet Explorer's sourceIndex property:

Retrieves the ordinal position of the object, in source order, as the object appears in the document's all collection.

sourceIndex (MSDN)

Put simply, this proprietary property holds the numeric index of a node within the "all collection" - an IE construct reflecting everything in the browser DOM. Thus, I wondered what the index would be for nodes in memory; that is, a node not yet - or previously - appended to the DOM.

A quick test proved the sourceIndex property has special values for each scenario:

• A value of -1 means the node has never been placed in the DOM.
• A value of 0 means the node has been removed from the DOM.*

* While the first case is pretty straight forward, the second (when 0) has an implied caveat. All array-like constructs are zero-based, and there is always a node at the zeroth index of document.all. Therefore, unless you know more about your node, a sourceIndex of 0 could be a false-positive and the node may still be in the DOM.

The generous folks at http://help.dottoro.com added my findings to their sourceIndex reference. Given their due diligence, I feel they've verified the application of my discovery.

I don't feel this proprietary property was intended as a node-placement indicator - hence the title of this blog entry. However, I've used it to great success as one, in a project where an IE only solution was needed (rare, I know).

Finally, for those interested in a cross browser solution, search stackoverflow.com to determine when a node is in the DOM.