cycleFinal.js

function cycle(...args){
  let [x,y] = [...args] 
  let els = Array.isArray(x) ? x : typeof y === 'undefined' ? [x] : [...filler(x,y)]
  let index = 0
  return {
   [Symbol.iterator]: function* (){      
      let _n = 0
      while ( _n < els.length){
        yield els[_n]
        _n++
      }
    },
    next: function() {
      if(index === els.length) // cycle
        index = 0
      return {value: els[index++], done: false}
    }
  }
}