Circular Array Range

circular_range.js

function ExtendedArray() {
  let arr = [];
  arr.push.apply(arr, arguments);
    
  /**
   * Returns a circulating range of an Array
   * @param index {Number} starting position
   * @param size {Number} size of the range
   * @param [reverse] {Boolean} reverse the range lookup
   * @return {Array} The returned array length will not exceed the length of the original array if size > arr.length
   **/
  arr.circularRange = function(index, size, reverse){
    // make a copy
    let a = this.slice(),
        // if index is out of bound start counting from 0
        f = index % a.length;
    return (reverse === true? a.splice(f - size + 1, size):a.splice(f)).concat(a).splice(0, size);
}

  return arr;
}

var arr = ExtendedArray(0,1,2,3,4,5,6,7,8,9);
console.log(arr.circularRange(9, 4)); // [9, 0, 1, 2]
console.log(arr.circularRange(1, 4, true)); // [8, 9, 0, 1]
console.log(arr.circularRange(9, 12)); // when size excedes length: [9, 0, 1, 2, 3, 4, 5, 6, 7, 8]