Q.

Welcome. In this kata, you are asked to square every digit of a number and concatenate them.
For example, if we run 9119 through the function, 811181 will come out, because 92 is 81 and 12 is 1.
Note: The function accepts an integer and returns an integer

A)

function squareDigits(num){
  return +String(num).split('').map(el => el * el).join('')
}

初めてmapを使う具体的な使い方はまだ分かりません.高次関数を学んだ私は再認識しなければならない.