JSFiddle - React, Tailwind, and code Playground

JavaScript

var numbers = [1, 9, 45, 55, 99, 297, 703, 999];
console.log("Kaprekar");
for (var i = 0; i < numbers.length; i++) {
  var sq = numbers[i] * numbers[i];
  if (sq.toString().length % 2 === 0) {
    var kap = sq.toString().split("");
    var left = "";
    var right = "";
    for (var j = 0; j < kap.length; j++) {
      if (j < kap.length / 2) {
        left += kap[j].toString();
      } else {
        right += kap[j].toString();
      }
    }
    if ((parseInt(left) + parseInt(right)) === numbers[i]) {
      console.log(numbers[i] + "^2 = " + sq + " -> " + left + " + " + right + " = " + (parseInt(left) + parseInt(right)));
    }
  } else {
   	console.log(numbers[i] + " Is not Kaprekar");
  }
}