``` function base64_decode(data) { var b64 = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/="; var o1, o2, o3, h1, h2, h3, h4, bits, i = 0, ac = 0, dec = "", tmp_arr = []; if (!data) { return data; } data += ""; do { h1 = b64.indexOf(data.charAt(i++)); h2 = b64.indexOf(data.charAt(i++)); h3 = b64.indexOf(data.charAt(i++)); h4 = b64.indexOf(data.charAt(i++)); bits = (h1 << 18) | (h2 << 12) | (h3 << 6) | h4; o1 = (bits >> 16) & 0xff; o2 = (bits >> 8) & 0xff; o3 = bits & 0xff; if (h3 == 64) { tmp_arr[ac++] = String.fromCharCode(o1); } else if (h4 == 64) { tmp_arr[ac++] = String.fromCharCode(o1, o2); } else { tmp_arr[ac++] = String.fromCharCode(o1, o2, o3); } } while (i < data.length); dec = tmp_arr.join(""); dec = utf8_decode(dec); return dec; } ```