You don't need a special API for this, this can be done with just normal javascript.
Example:
var doc = currentDocument;
var item = doc.getValue("Body");
print("Body: " + typeof item);
console:
HTTP JVM: Body : com.ibm.xsp.model.domino.wrapped.DominoRichTextItem
typeof is a standard method of javascript as given the loosely bound nature of its variables it is required from time to time, epically in validation.
Hope this helps.