static deepCopy(arr) {
    let newArr = Array();

    for (let i = 0; i < arr.length; i++) {
      let item = arr[i];

      if (item instanceof Array) {
        newArr[i] = ArrayHelper.deepCopy(item);
      } else {
        newArr[i] = item;
      }
    }

    return newArr;
  }
Copies a an n-dimensional array.

@param {Array} arr The array to be copied.
@returns {Array} The copy.