JSFiddle - React, Tailwind, and code Playground

JavaScript

const start = '81';
const govnyak = start.split('').reduce((a, b) => parseInt(a) + parseInt(b));
const sho = Math.pow(govnyak, 2);
console.log(sho);
console.log(Math.pow(start.split('').reduce((a, b) => parseInt(a) + parseInt(b)), 2));