docs: function cal_arrayPush(n) {
    function toFib(x, y, z) {
      x.push((z < 2) ? z : x[z - 1] + x[z - 2])
      return x
    }
  
    var arr = Array.apply(null, new Array(n)).reduce(toFib, [])
    var len = arr.length
    return arr[len - 1] + arr[len - 2]
  }