There are tons of "Javascript Developers" who have no experience and about as much knowledge of the front-end. They usually make up the large crowd of "web cons

There are tons of "Javascript Developers" who have no experience and about as much knowledge of the front-end. They usually make up the large crowd of "web consultants" that offer to make you a website for just $300 and then deliver wordpress with some skin they bought from somewhere. The web specs are millions of pages of legalese (and that's without mentioning things like WebGL which are handled by groups other than w3c). Learning all the stuff required for building a modern application on the web takes a long time. In addition, the incompatibilities and inconsistencies (between both browsers and browser versions) paired with the inconsistencies of much of the tooling and frameworks (though that has gotten much better in the past couple years) leads to a frustrating experience. If you need an actual web app and want to hire a knowledgeable developer who's willing to learn everything and not burn out from dealing with all the frustrating parts, it's very likely that you'll wind up paying more than for a back-end dev with similar amounts of experience.