I cannot separate web development and mobile development. Mobile devices will become more and more like Desktop devices : less native applications, more web applications. Even if Firefox OS has given up, the work of Google on Progressive Web Apps and the work of Mozilla, Google and Microsoft on Service Worker mean they will be ok to deploy more and more mobile web application.

Mobile device is a very specific platform as the internet connection is very capricious, and even with its quad-core processors, it is small and has less power than a classical laptop. Keeping that in mind may let you being a great mobile web developer.

PS: hope my english worth reading.

You can't be great at everything, but there's value both in general knowledge and specific knowledge. Try and know a little about most things, and a lot about a few areas that are most valuable to you -- either because you enjoy them, or because you get paid well because of it.

I do both native mobile and full-stack web development, and I consider myself good at both, but obviously someone who has been living and breathing iOS development for the last ten years should be better at iOS development than I am, and someone focuses intensely on front-end development may know more about CSS FlexBox and ServiceWorkers and Angular / React than I do. That's ok.

Incidentally, that's true of more than technology -- having generalized knowledge of business and specific knowledge of a few industries is also valuable.

If you have to choose, I'd say web because a lot of sites are moving to progressive web apps as opposed to native mobile apps. The web is getting smarter and more capable. That said, there's also a lot of value to learning mobile development. It really depends on what you want to do or where you work/want to work. This is just my opinion if you're trying to choose one as a focus. There is a lot out there, so you don't even need to limit yourself, just give yourself stretch goals for what you'd like to learn, it's just a matter of where to start.

Both. A good way of going about it is learning React for front end web development. Those same skills can be applied in creating mobile apps through React Native.

I really think you can do more than both - let's throw in backend code there as well. When you know how you can write backend code, front-end code (both on the mobile and the web) and do some devops as well, you become super valuable in the industry and more than that, you'll feel happy.

That being said, it's important focus on one of the technologies at a time. I started out as a backend developer (which is what I'm still the strongest at), but every single day I watched my team's front-end dev's commits and picked up front end development over a period of six months. By the end of 2017, I hope to pick up mobile development as well.

Well depends, nowadays if you are a good javascript developer can be a mobile developer, not the same quality as native mobile developer, but with javascript there are tools to make apps in an easy way.

If your focus is to make web pages, or web apps and you like all the web ecosystem go for a javascript developer. If you want to make amazing mobile apps, native for iOS and Android go for mobile developer.

It depends on the need of company. if need ,both.