Lib/function for One Time Padding strings

otp.js

(() => {
    const OTP = (() => {
        function xorStrings(a, b) {
            let c = "";

            for (let i = 0; i < a.length; i++)
                c += String.fromCharCode(a.charCodeAt(i) ^ b.charCodeAt(i));

            return c;
        }

        function padkey(key, length) {
            let padded = key;
            while (padded.length < length)
                padded += key;

            return padded.substr(0, length);
        }

        function transform(message, key) {
            return xorStrings(message, padkey(key, message.length));
        }

        return transform;
    })();

    if (typeof window !== 'undefined') {
        window.OTP = OTP;
    }
    if (typeof module !== 'undefined') {
        module.exports = OTP;
    }
})();

const OTP = require('./otp.js');
const message = 'anything';
const key = 'a secret';

//encrypt
const encrypted = OTP(message, key);

//decrypt
const result = OTP(encrypted, key);