Chrisir, we are teaching Javascript to Elementary School students. They all use Chromebooks, iPads, or similar. A 100% browser based solution is a requirement. In addition, the students do not bring their chromebooks home, but instead have home computers that will login into the cloud environment.
The p5.js platform suits the needs very well. But at this age, additional tools such as a grid with mouse location aids in their visualization of drawing actions. I’m adding a color picker as well, which will give them an each way to set colors of objects created.