You may recall back at SMX Seattle earlier this year, Google's Matt Cutts talked at length about paid links. He touched upon the topic of Google being able to read javascript after giving out advice for so long to use javascript as a way to keep Google from reading paid links.

When asked about this, Matt said Googlebot had gotten smarter. He noted that Google began changing its messaging on the subject around 2007-2008 to stop mentioning javascript but to nofollow or do a redirect through a URL which is blocked through robots.txt.

Cutts noted that even on the onclick in javascript, the crawl and indexing team had submitted code so that it would respect a rel="nofollow". So you can put a rel="nofollow" attribute on a link that's running in javascript, and more often than not, Google will make sure it doesn't flow pagerank even if they're executing the javascript.

Cutts did say, however, that if you want to be completely safe, to nofollow or link through things that are blocked.

Cutts revisited the topic in a recent upload to the Google Webmaster Central YouTube channel, in response to the following user question:

Now that Google can crawl JavaScript links, what is going to happen with all those paid links that were behind JavScript code? Will Google start penalizing them?

Matt reiterated that Google has gotten better at crawling javascript, and that URLs you put into javascript that you didn't think would be crawled, might now possibly be crawled and indexed. He says the vast majority of people who do javascript links are ad networks and that Google handles these very well.

He then reiterated the use of nofollow, even within the javascript code, and the use of robots.txt to block out URls, and redirects.

"We find that the vast majority of paid links are typically not done with javascript," says Cutts. "They're typically completely straight text links. so that's where we've been spending the vast majority of our time."

Cutts says that Google is not currently penalizing paid javascript links, but they may start looking down the line. He says it hasn't been a big issue at all in his experience though.

"If you're selling text links, just make sure they don't flow page rank and they don’t effect search engines," he says.