First, let's understand one thing that, gone are the days when there was a clear division between designer and website developer.
The role of a designer was to design and convert the website into HTML. That's that. But the time has changed and the line between developer and designer has tuned blur.
So, if you are a designer and you want to become a good front-end developer (there is great career for front-end developer) you should learn MEAN Stack (At least Angular).