Get last digit of an EAN/GTIN 13 in JavaScript

last-digit-ean13.js

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
}

console.log(getLastEan13Digit('340093903576'))

Thanks