SEO question regarding a specific javascript event – advanced stuff

Hi
I’m thinking about implementing a javascript “on before unload” event.

Its purpose - if someone is leaving my site, it will direct him to another page.

My question is – do you see any SEO damage this could do to my site? Even if there is a %0.00001 chance that it could harm my site’s SEO I’d need to pass.

This script is very close to what I’m talking about: (but not entirely).
add www.hunlock.com/blogs/Mastering_The_Back_Button_With_Javascript

What do you say, oh great SEO lords?

 

will it also do same with Robots ?

 

JavaScript executes on a client's machine so it won't affect the SEO aspect at all since Google doesn't execute JS, as far as I know (I've tested this a while ago).

 

Robots.txt can't contain JavaScript so your quesiton is senseless.

 

I am talking about crawlers

 

Crawlers do not execute JS. Don't worry. For now. Maybe some day they will.