I don't know how anyone can place any stock in an index that says JavaScript has declined in the past year, and currently ranks lower than Perl. There is scarcely a web-page served (with the exception of here at the Monastery) that doesn't contain <script> tags. And that doesn't even count the other uses of JavaScript such as Node.JS, driving Selenium, and so on. Sure, we love Perl, but for Tiobe to show a decline for JavaScript, and to rank it outside of the top-5, I think, shows that the index lacks relevance. I even looked to see if the index possibly has an entry for ECMAScript that might be consuming some of JavaScript's stats, but found no such entry, though the Tiobe explanation page does mention ECMAScript as one of the languages tracked.
StackOverflow currently shows 199.6k followers of the Javascript tag, and 12k followers of the Perl tag. It seems to me Tiobe is tracking data that has a low correlation to what people take the index to be an indicator for.