I am not sure what you are planning to build or trying to solve next. Swift is an excellent language and still evolving at a very fast pace. Swift has been a choice for development for iOS development for ever since it's introduced (with lot of rough edges).
Swift is open source and cross platform as well. Companies like IBM heavily advocates Swift and very active in the community. Frameworks like Kitura helps you to build web apps using Swift. The tooling and frameworks many not as extensive and mature as node + express or Rails but it is still worth looking at if you are interested.
If you are interested in iOS development, Swift is a great choice and get started there. You should be looking at ReactNative to leverage your experience with JavaScript tooling and build cross platform apps for Android and iOS. Certainly a platform level knowledge is required to build something solid.