Echo JS 0.11.0

appreciate the effort, but this is really not that useful IMHO.

1 - setInterval is very well known and there should be a real compelling reason to use a custom wrapper api.

2 - the library usage has side-effects... if two dependencies/files use this without coping the instance- things will get unpredictable


3 - you're making SetInterval instances via object copy (prototype design pattern)- the created cloned instance is a new variable, which is what you set out to avoid.
3* - if you prefer objects over the interval return variable, it would have been simpler to use classes (though I still prefer the base API):

class Interval {
  constructor(fn, interval) {
    this.timer = setInterval(fn, interval);
  }
  clear() {clearInterval(this.timer);}
}