How to handle context menu cancellation event

[zinon]

I am trying to implement a system to mask affiliated links
of a web page. I can handle user's right click with
oncontextmenu event and mask the link without any problem
but when user cancels context menu, link value is been
changed.

link.oncontextmenu = function () {
  link.href = "http://......";          
}

I cannot find a way to handle when user cancel context
menu to change link's value into its original value.

Any idea?

Thanks.