javascript ean13 checksum generate
function getLastEan13Digit(ean) {
if (!ean || ean.length !== 12) throw new Error('Invalid EAN 13, should have 12 digits');
const multiply = [1, 3];
let total = 0;
ean.split('').forEach((letter, index) => {
total += parseInt(letter, 10) * multiply[index % 2];
});
const base10Superior = Math.ceil(total / 10) * 10;
return base10Superior - total;
}