I've been working at web-based startups for over 10 years now, and I know VERY few devs who only know JS. Most are also proficient (or at least have working kno

I've been working at web-based startups for over 10 years now, and I know VERY few devs who only know JS. Most are also proficient (or at least have working knowledge of) whatever other languages we're using. Usually JVM-based like Java, Kotlin, Scala or something else like Ruby or Elixir. Everywhere I've been, we always "choose the right tool for the job". Recently, making apps that can run across every OS and in the browser, the right tool for the job has been JS (well, TypeScript these days, but same thing).