function aggregateElements (elements) {
  function aggregate (arr, initValue, func) {
    let val = initValue
    for (let i = 0; i < arr.length; i++) {
      val = func(val, arr[i])
    }

    console.log(val)
  }

  aggregate(elements, 0, (a, b) => a + b)
  aggregate(elements, 0, (a, b) => a + 1 / b)
  aggregate(elements, '', (a, b) => a + b)
}

aggregateElements([1, 2, 3])