> Read this tutorial: https://www.scirra.com/tutorials/73/supporting-multiple-screen-sizes
> Short version: Use Scale Outer or Scale Inner for resolution/aspect ratio and Anchor behavior for the HUD elements
That is the best way above, but perhaps more time intensive than what you need every time.
My quick and dirty preference is:
Screen resolution: 480x720
Fullscreen in Browser: Letterbox Scale (not integer!)
This will give you minimal black bars on the screen as it is a midrange setting. I'd rather have a little bit of black bars on the side (if any) than have the screen look a way it is not intended or show something outside the program window which could make it look really bad. Like I said, it's quick and dirty, but not bad. I believe people are a lot more interested in the look of something and what it does than whether or not you used every pixel on the screen doing it. Of course if every pixel counts, be ready to program for every situation-and good luck with that!
CocoonJS does not support letterbox scale, and will revert to scale outer by default
Also supporting multiple screen size is something that people should look into I think, some games it can be really simple, others a little more complicated, and other just impossible, being able to think about it is still nice