Use function to generate and validate Luhn mod N algorithm checksums for strings

use-luhn.js

export default (chars = 'ABCDEFGHJKMNPQRSTUVWXYZ0123456789') => {
	const checksum = input => {
		const { sum } = input.split('').reverse().reduce((acc, char) => {
			const addend = acc.factor * chars.indexOf(char);
			acc.factor = acc.factor === 2 ? 1 : 2;
			acc.sum += Math.floor(addend / chars.length) + (addend % chars.length);
			return acc;
		}, { sum: 0, factor: 2 });
		const remainder = sum % chars.length;
		return chars[(chars.length - remainder) % chars.length];
	};
	
	const generate = input => `${input}${checksum(input)}`;
	
	const validate = input => input.slice(-1) === checksum(input.slice(0, -1));
	
	return { generate, validate };
};