JavaScript: Encode to Base64

Once again, I will not take credit of this one...

// ***
// Encode to Base64
// Warning: Do not use for larger content as the loop might take a while
// ***
function base64Encode(data)
{
if (typeof(btoa) == 'function') return btoa(data);
var b64_map = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=';
var byte1, byte2, byte3;
var ch1, ch2, ch3, ch4;
var result = new Array();
var j=0;
for (var i=0; i byte1 = data.charCodeAt(i);
byte2 = data.charCodeAt(i+1);
byte3 = data.charCodeAt(i+2);
ch1 = byte1 >> 2;
ch2 = ((byte1 & 3) << 4) | (byte2 >> 4);
ch3 = ((byte2 & 15) << 2) | (byte3 >> 6);
ch4 = byte3 & 63;

if (isNaN(byte2)) {
ch3 = ch4 = 64;
} else if (isNaN(byte3)) {
ch4 = 64;
}

result[j++] = b64_map.charAt(ch1)+b64_map.charAt(ch2)+b64_map.charAt(ch3)+b64_map.charAt(ch4);
}

return result.join('');
}