All the lessons and exercises are well structured and divided into different sections.
If you already have some JS skills and knowledge, you can also skip the first levels. So it can be more a wiki instead an exercise
Because the app works offline, you can use it anywhere you want. It's also completely free, just expect some not annoying popup ads after finishing levels.
Feel free to download the app!
Or if you want to try SoloLearn for JS instead try this.