Javascript to Inform of redirection

I am trying to ensure that on my external links page, when links are clicked, the user is informed that they are now leaving my site and then are redirected to the outside site. I would prefer to use javascript or something else that does not require the server. But I cannot figure out how to do this simply using javascript. Likewise, I need the code to not reside in the link because new links will be added by nontech people and it should be as simple as possible for them to add new links. Any suggestions?