JavaScriptでBase64をデコードするには次のように書く。
var b64_table = [
'\x00','\x01','\x02','\x03','\x04','\x05','\x06','\x07',
'\x08','\x09','\x0A','\x0B','\x0C','\x0D','\x0E','\x0F',
'\x10','\x11','\x12','\x13','\x14','\x15','\x16','\x17',
'\x18','\x19','\x1A','\x1B','\x1C','\x1D','\x1E','\x1F',
'\x20','\x21','\x22','\x23','\x24','\x25','\x26','\x27',
'\x28','\x29','\x2A','\x2B','\x2C','\x2D','\x2E','\x2F',
'\x30','\x31','\x32','\x33','\x34','\x35','\x36','\x37',
'\x38','\x39','\x3A','\x3B','\x3C','\x3D','\x3E','\x3F',
'\x40','\x41','\x42','\x43','\x44','\x45','\x46','\x47',
'\x48','\x49','\x4A','\x4B','\x4C','\x4D','\x4E','\x4F',
'\x50','\x51','\x52','\x53','\x54','\x55','\x56','\x57',
'\x58','\x59','\x5A','\x5B','\x5C','\x5D','\x5E','\x5F',
'\x60','\x61','\x62','\x63','\x64','\x65','\x66','\x67',
'\x68','\x69','\x6A','\x6B','\x6C','\x6D','\x6E','\x6F',
'\x70','\x71','\x72','\x73','\x74','\x75','\x76','\x77',
'\x78','\x79','\x7A','\x7B','\x7C','\x7D','\x7E','\x7F',
'\x80','\x81','\x82','\x83','\x84','\x85','\x86','\x87',
'\x88','\x89','\x8A','\x8B','\x8C','\x8D','\x8E','\x8F',
'\x90','\x91','\x92','\x93','\x94','\x95','\x96','\x97',
'\x98','\x99','\x9A','\x9B','\x9C','\x9D','\x9E','\x9F',
'\xA0','\xA1','\xA2','\xA3','\xA4','\xA5','\xA6','\xA7',
'\xA8','\xA9','\xAA','\xAB','\xAC','\xAD','\xAE','\xAF',
'\xB0','\xB1','\xB2','\xB3','\xB4','\xB5','\xB6','\xB7',
'\xB8','\xB9','\xBA','\xBB','\xBC','\xBD','\xBE','\xBF',
'\xC0','\xC1','\xC2','\xC3','\xC4','\xC5','\xC6','\xC7',
'\xC8','\xC9','\xCA','\xCB','\xCC','\xCD','\xCE','\xCF',
'\xD0','\xD1','\xD2','\xD3','\xD4','\xD5','\xD6','\xD7',
'\xD8','\xD9','\xDA','\xDB','\xDC','\xDD','\xDE','\xDF',
'\xE0','\xE1','\xE2','\xE3','\xE4','\xE5','\xE6','\xE7',
'\xE8','\xE9','\xEA','\xEB','\xEC','\xED','\xEE','\xEF',
'\xF0','\xF1','\xF2','\xF3','\xF4','\xF5','\xF6','\xF7',
'\xF8','\xF9','\xFA','\xFB','\xFC','\xFD','\xFE','\xFF'
];
function b64_decode_char(c){
if('A' <= c && c <= 'Z'){
return c.charCodeAt(0) - 'A'.charCodeAt(0);
}
if('a' <= c && c <= 'z'){
return c.charCodeAt(0) - 'a'.charCodeAt(0) + 26;
}
if('0' <= c && c <= '9'){
return c.charCodeAt(0) - '0'.charCodeAt(0) + 52;
}
if(c == '+'){
return 62;
}
if(c == '/'){
return 63;
}
if(c == '='){
return 0;
}
error(true, "invalid base64 character. " + c);
return -1;
}
function b64_decode(str){
var decoded = "";
for(var i=0; i> 16 & 0xff];
decoded += b64_table[buf >> 8 & 0xff];
decoded += b64_table[buf & 0xff];
}
var ex = 0;
if(str.charAt(str.length-1) == '=') ex++;
if(str.charAt(str.length-2) == '=') ex++;
if(ex != 0){
decoded = decoded.substring(0, decoded.length-ex);
}
return decoded;
}
errorは中で例外を投げている。