Want to know clearly about Javascript

Yes you can be a Fullstack Javascript Developer. The most common stack used by Fullstack Javascript Developers is the MEAN stack (MongoDB, Express, Angular.js Node.js).

MongoDB - This is a back end database solution that is a noSQL database (Like mySQL but non-relational method of data storage)

Express JS - This is a light-weight web application framework for Node.js that helps minimise code replication, speed up your workflow and automatically handles a lot of repeatitive work related to Node.js.

Angular.js - This is a Javascript Framework that extends HTML attributes with directives, and helps bind data to HTML with expressions.

Node.js - This is a Javascript solution to a backend server programmng language such as PHP or Python.

It is not as simple as just learning Javascript like many people say, but essentially you will be using one language throughout the whole stack which is Javascript.

Personally myself I am a LAMP stack developer (Linux, Apache, mySQL/MongoDB, PHP/Python). I work with someone who is a Fullstack Javascript Developer and he loves doing everything in Javascript, it has it's pros and cons though hence why we are both employed for different specality parts of our companies web infastructure.