From easy to intermediate:
####Clock
- Basic JS
- DOM selections
- CSS transitions
####Particles
- p5 library (uses HTML5 Canvas)
- JS objects/constructors/prototypes
####Speech Recognition
- http-server
- DOM manipulation
- event-listeners
- map
- API
####Search
- fetch browser API (ES6 promises)
- regex
- event-listeners
- map
- CSS child selectors
- CSS transform
See Javascript30 for more short demos and inspiration.