Which should I have to learn? PHP or JavaScript?

Question

As I heard that most of the things (website (frontend, backend), webapps, mobile apps etc.) can be made by JavaScript and PHP is used for backend. If I want to be a good web developer, then which should be my first choice. Is it necessary to learn both?

In addition, how is .NET?

I don't know if I said wrong or right. As I'm a learner forgive me for any mistake. Thank you in advance.