WOL Apgar routine in Javascript

apgar.js

function apgar(s) {  
    if (s.length != 8) return false;
    var s = s.split(''), o = [];
    var u = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789./';
    for(var i = 0; i <= 7; i++) {
        var a = s[(8 - i)], r = ((i == 0) ? 0 : a.charCodeAt(0));
        var j = s[i].charCodeAt(0), x = ((j & 1) ? (j << 1) & r : j ^ r);
        var k = (x & 0x3f), f = u.substring(k, (k + 1));
        o.push(f);
    }
    return o.join('');
}

console.log('apgar', apgar('password')); // WaIMMsbf