Encrypt and decrypt text with a password and this simple yet effective cypher

RollingCypher.js

function RollingCypher() {
    var chars = " qwertyuiopasdfghjklzxcvbnmQWERTYUIOPASDFGHJKLZXCVBNM1234567890!@#$%^&*()_+-=[]\\{}|;':\",./<>?`~\t\r\n";
    chars = chars.concat(chars.concat(chars));

    function encrypt(s, p) {
        var o = "";
        s = s.split('');
        p = p.split('');
        for (var i = 0; i < s.length; i++) {
            o += chars[chars.indexOf(s[i]) + chars.indexOf(p[i % p.length])];
        }
        return o;
    }

    function decrypt(s, pass) {
        var o = "";
        s = s.split('');
        pass = pass.split('');
        for (var i = 0; i < s.length; i++) {
            o += chars[chars.lastIndexOf(s[i]) - chars.indexOf(pass[i % pass.length])];
        }
        return o;
    }

    this.encrypt = encrypt;
    this.decrypt = decrypt;
}