[alkonaut]

Google and other search engine crawlers view pages much like browsers these days, see e.g. http://searchengineland.com/tested-googlebot-crawls-javascri... Not sure what the ranking penalty might be. Would guess it's small to none.

I'm surprised even 10% of sites show anything these days. I get a lot of broken sites just by disabling tracking and ads.

I can imagine disabling js would be much like disabling half of the html tags.

[m0th87]

In my experience, this isn't really true. Google still can't crawl most non-trivial javascript-powered apps, and if it doesn't work, there's little insight on what you need to tweak to get it working. It hasn't been able to crawl our javascript-powered parts of the site across two major architectures without prerender, and I know a lot of other companies with the same issue.