Create loop

cycle.js

var aList = ['A','B','C','D','E'];

/**
 *
 * @param  {Array} arr
 * @return {Generator}
 */
function* cycle(arr) {
  const arr = [...arr];
  let i = 0;
  while (true) {
    i = (i + ((yield arr[i]) || 1)) % arr.length
  }
}

let rCycle = cycle(aList);

console.log(rCycle);
console.log(rCycle.next());
console.log(rCycle.next());
console.log(rCycle.next(-1));
console.log(rCycle.next(2));




function looper( arr ){

  arr.loop_idx = 0;

  // return current item
  arr.current = function(){
    this.loop_idx = ( this.loop_idx ) % this.length;// no verification !!
    return arr[ this.loop_idx ];
  };

  // increment loop_idx AND return new current
  arr.next = function(){
    this.loop_idx++;
    return this.current();
  };

  // decrement loop_idx AND return new current
  arr.prev = function(){
    this.loop_idx += this.length - 1;
    return this.current();
  };
}


console.log(aList.current());// -> A
console.log(aList.next());// -> B
console.log(aList.next());// -> C
console.log(aList.next());// -> D
console.log(aList.next());// -> E
console.log(aList.next());// -> A
console.log(aList.pop()) ;// -> E
console.log(aList.prev());// -> D
console.log(aList.prev());// -> C
console.log(aList.prev());// -> B
console.log(aList.prev());// -> A
console.log(aList.prev());// -> D