Base64 编码解码算法(JS版)[备忘录]
<html>
<HTML>
<HEAD>
<TITLE>Base64</TITLE>
<script type='text/javascript'>
var BASE64_ENCODE_CHARS = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
var BASE64_DECODE_CHARS = [ -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 62, -1, -1, -1, 63, 52, 53, 54, 55, 56, 57,
58, 59, 60, 61, -1, -1, -1, -1, -1, -1, -1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, -1, -1, -1, -1, -1, -1, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44,
45, 46, 47, 48, 49, 50, 51, -1, -1, -1, -1, -1 ];
function encodeBase64(str) {
var c1, c2, c3, i = 0, len = str.length, out = [];
while (i < len) {
c1 = str.charCodeAt(i++) & 0xff;
if (i == len) {
out.push(BASE64_ENCODE_CHARS.charAt(c1 >> 2));
out.push(BASE64_ENCODE_CHARS.charAt((c1 & 0x3) << 4));
out.push('==');
break;
}
c2 = str.charCodeAt(i++);
if (i == len) {
out.push(BASE64_ENCODE_CHARS.charAt(c1 >> 2));
out.push(BASE64_ENCODE_CHARS.charAt(((c1 & 0x3) << 4) | ((c2 & 0xF0) >> 4)));
out.push(BASE64_ENCODE_CHARS.charAt((c2 & 0xF) << 2));
out.push('=');
break;
}
c3 = str.charCodeAt(i++);
out.push(BASE64_ENCODE_CHARS.charAt(c1 >> 2));
out.push(BASE64_ENCODE_CHARS.charAt(((c1 & 0x3) << 4) | ((c2 & 0xF0) >> 4)));
out.push(BASE64_ENCODE_CHARS.charAt(((c2 & 0xF) << 2) | ((c3 & 0xC0) >> 6)));
out.push(BASE64_ENCODE_CHARS.charAt(c3 & 0x3F));
}
return out.join('');
}
function decodeBase64(str) {
var c1, c2, c3, c4, i = 0, len = str.length, out = [];
while (i < len) {
/* c1 */
do {
c1 = BASE64_DECODE_CHARS[str.charCodeAt(i++) & 0xff];
} while (i < len && c1 == -1);
if (c1 == -1)
break;
/* c2 */
do {
c2 = BASE64_DECODE_CHARS[str.charCodeAt(i++) & 0xff];
} while (i < len && c2 == -1);
if (c2 == -1)
break;
out.push(String.fromCharCode((c1 << 2) | ((c2 & 0x30) >> 4)));
/* c3 */
do {
c3 = str.charCodeAt(i++) & 0xff;
if (c3 == 61)
return out.join('');
c3 = BASE64_DECODE_CHARS[c3];
} while (i < len && c3 == -1);
if (c3 == -1)
break;
out.push(String.fromCharCode(((c2 & 0XF) << 4) | ((c3 & 0x3C) >> 2)));
/* c4 */
do {
c4 = str.charCodeAt(i++) & 0xff;
if (c4 == 61)
return out.join('');
c4 = BASE64_DECODE_CHARS[c4];
} while (i < len && c4 == -1);
if (c4 == -1)
break;
out.push(String.fromCharCode(((c3 & 0x03) << 6) | c4));
}
return out.join('');
}
function utf16to8(str) {
var out, i, len, c;
out = '';
len = str.length;
for (i = 0; i < len; i++) {
c = str.charCodeAt(i);
if ((c >= 0x0001) && (c <= 0x007F)) {
out += str.charAt(i);
} else if (c > 0x07FF) {
out += String.fromCharCode(0xE0 | ((c >> 12) & 0x0F));
out += String.fromCharCode(0x80 | ((c >> 6) & 0x3F));
out += String.fromCharCode(0x80 | ((c >> 0) & 0x3F));
} else {
out += String.fromCharCode(0xC0 | ((c >> 6) & 0x1F));
out += String.fromCharCode(0x80 | ((c >> 0) & 0x3F));
}
}
return out;
}
function utf8to16(str) {
var out, i, len, c;
var char2, char3;
out = "";
len = str.length;
i = 0;
while (i < len) {
c = str.charCodeAt(i++);
switch (c >> 4) {
case 0:
case 1:
case 2:
case 3:
case 4:
case 5:
case 6:
case 7:
// 0xxxxxxx
out += str.charAt(i - 1);
break;
case 12:
case 13:
// 110x xxxx 10xx xxxx
char2 = str.charCodeAt(i++);
out += String.fromCharCode(((c & 0x1F) << 6) | (char2 & 0x3F));
break;
case 14:
// 1110 xxxx 10xx xxxx 10xx xxxx
char2 = str.charCodeAt(i++);
char3 = str.charCodeAt(i++);
out += String.fromCharCode(((c & 0x0F) << 12) | ((char2 & 0x3F) << 6) | ((char3 & 0x3F) << 0));
break;
}
}
return out;
}
function doIt() {
var sourceValue = document.getElementById('source').value;
document.getElementById('output').value = encodeBase64((sourceValue));
document.getElementById('decode').value = utf8to16(decodeBase64(sourceValue));
}
</script>
<body>
Source :
<br>
<textarea id="source" style='width: 500; height: 80;'></textarea>
<br>
<br> base64 Encode :
<br>
<textarea id="output" style='width: 500; height: 80;'></textarea>
<br>
<br> base64 Eecode :
<br>
<textarea id="decode" style='width: 500; height: 80;'></textarea>
<br>
<br>
<input type=button value="Transcoding" onclick="doIt()">
</body>
</html>
备注：JS取得的String编码是UTF-16，但是这个Base64支持的是8位(1字节) 所以为了支持中文，在编码前进行了16>8的转换，解码的时候进行了8>16的转换。如果不考虑中文可以不加这个转换。
