JSFiddle - React, Tailwind, and code Playground

JavaScript

var summa2;

function fun (block1, block2, block3, block4) {
return summa2 = Number(block1) + Number(block2) + Number(block3) + Number(block4)
}
var block1 = prompt('Число 1: ');
var block2 = prompt('Число 2: ');
var block3 = prompt('Число 3: ');
var block4 = prompt('Число 4: ');
document.write('Сумма введенных чисел равна: ' + fun(block1, block2, block3, block4));

var summa = fun(block1, block2, block3, block4);

alert(summa);

alert('summa2: '+summa2)