Do (Google) robots / crawlers follow links if the 'rel="nofollow"' is set through javascript?

I want to keep bots from following my external links through rel=nofollow. I have 2 questions about it:

1) Does this really help my page ranking (I heard a SEO guy saying this, as it the page ranking should go up as the probability is lower that the user leaves the page)

2) Does it work when the rel=nofollow is set through javascript in the $(document).ready() function?

EDIT: thanks for the suggestions so far - to go more into detail to 1:

how can the robot know(...)?

The robot knows this because he knows the page ranking of the page that you link to, and if it is high the probability is high that you follow this link and so by leave my page. That's why it is supposed to be good if you have more incoming than outgoing links, where of course incoming links from high-ranked pages count more than incomi开发者_如何学运维ng links from low-ranked websites. on the other hand outgoing links to high-ranked pages are supposed to increase the probability that the user leaves... but I am no expert in this that's just what this SEO guy was telling

EDIT 2 Question is if it improves my Google pageranking if I put rel="nofollow" to external links, and - in case it improves my page ranking - if this still works through setting it with javascript. Thanks in advance

1. It's possible. Your pages will flow pagerank internally, so having more outbound links will decrease the pagerank you flow to your own pages.

2. Google is capable of reading javascript, and will honor a nofollow on dynamically created links, however, I am not sure if it works when dynamically adding nofollow on 'static' links.

Of course, there's much speculation when it comes to SEO.

1. I doubt
2. No, it doesn't work. Bots generally don't execute JavaScript code.

1. What?

   the page ranking should go up as the probability is lower that the user leaves the page

   How should a robot know this?

2. Robots don't process JavaScript, rel="nofollow" has to be present in the source markup as it is sent to the client.

And to add: rel="nofollow" does not guarantee that a link is not followed or added as link to the other page to build up page rank (the real process is much more complex); that depends on the robot/search engine.

Adding a rel="nofollow" will not stop the bot following the link. but it will stop the bot giving any of your page rank to that link.

Oh and as said before mostly bots do not execute JavaScript. I belive google have been playing around with one that dose, but this is the exception not the norm.

1) The more pages that you link out to, the more it affects your authority ratio, you essentially want more linking in that you link out. CTR is tracked by google analytics and this is factored into their essentially blackbox search ranking magic.

2) Whilst it's commonly thought that robots don't process JavaScript, this is wrong, google's current generation of robots are ajax aware.

I came here looking for an answer to this question myself. (Thanks Andre!)

I can attest to Google following links with href="javascript:..." URLs, and going to the correct pages, so that is no defense against unwanted link-crawling. I have also seen search result snippets include text inserted by javascript, so there is ample evidence of Google processing javascript.

If the links are internal, proper use of robots.txt would be the preferred, easier, and more bandwidth-efficient answer, of course, if you have access to that. (We don't on the server in question, thus my own search for answers.)

I shall be adding nofollow via javascript.