I think your asking for a web framework. As of right now there are 3 big ones:
- FCC teaches this in its curriculum
- Hands down the most popular front-end framework
- Large amount of job opportunities
- Backed by Facebook
- Not a complete solution (only cares about how to render the view)
- Angular - A Front-end framework to build web-apps.
- Not as popular as React due to its complexity, but very capable and more of a complete solution than React
- Built from the ground up with the lessons learned from legacy Angularjs (the older version)
- Great tooling (possibly the best)
- Typescript and RXJS based
- Backed by Google
- Much more complex than React or Vue
- Vue - A versatile, simple front-end framework
- Great tooling
- Supported by the community
- Know to be easier and more approachable than Angular or React.
- limited job opportunities, regardless of the “hype” around the frameworks popularity.
Regardless, today it’s more likely to be using a front-end framework to build web-apps/complex web-sites than using something else.
Goodluck and keep developing
To add to bradtaniguchi’s point, if you learn either React or Angular and are interested in building mobile apps, you can venture into mobile development with React Native for the former, and Ionic for the latter.