I am writing a program that add the sum of squares of each digit in that number until the sum become one single integer. For example: 203 -> 13 -> 10 -> 1 -> 1

I have been figured out the first step but I am stuck to proceed to reach one single integer, Can anyone helps

```
function squareSum(numbers) {
var numbers = Array.from(String(numbers), Number);
var square_sum = [];
for (let i = 0; i < numbers.length; i++) {
square_sum.push(numbers[i] * numbers[i]);
}
var SquareSum = 0
for (let j = 0; j < square_sum.length; j++) {
SquareSum = SquareSum + square_sum[j];
}
return SquareSum;
}
console.log(squareSum(203));
```