Sometimes we want to know, what tech stack a website uses. Say facebook, it uses PHP in it's tech stack. Most websites nowadays use Rails (atleast I think so). We can easily find out if a website uses Rails, with a simple client-side check.
$ sign. All rails apps, use rails.js as a dependency, so if you ever see it on a site, it is most likely that specific site is a Rails app.You can test it on Coderwall itself! (yes, Coderwall is a rails app).