How to check in Javascript if one element is contained within another

How can I check if one DOM element is a child of another DOM element? Are there any built in methods for this? For example, something like:

if (element1.hasDescendant(element2)) 

or

if (element2.hasParent(element1)) 

If not then any ideas how to do this? It also needs to be cross browser. I should also mention that the child could be nested many levels below the parent.