js_arr_sum.js

class DecoratedClass {
  constructor(arr) {
    this.arr = arr;
    this.total = 0;
  }

  sum() {
    this.arr.map(el => { this.total += el })

    return this.total;
  }
}

const arr = [1, 2, 3];
dc = new DecoratedClass(arr);

dc.arr;
dc.sum();