Armstrong number using prompt sync

Question

var num = require("prompt-sync")()("message")
const armstrongNumber = (num) => {

  const toArray = num.toString().split('').map(Number);

  const newNum = toArray.map(a => {return a**3}).reduce((a, b) => a + b); //Here we need to change the expontenial power accordingly to sum of own digits 

  if(newNum == num){
      console.log('This is an armstrong number');
  }else{
      console.log('This is not an armstrong number');

  }
}
armstrongNumber(num)

how to do if I use loop statements in the function? I used while loop in the function, but then in the console most of the armstrong values returning it as 'This is not an armstrong number'