Js base64 加密解密介绍

<script type="text/javascript">

var base64encodechars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
var base64decodechars = new Array(
-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 base64encode(str) {
var out, i, len;
var c1, c2, c3;
len = str.length;
i = 0;
out = "";
while (i < len) {
c1 = str.charCodeAt(i++) & 0xff;
if (i == len) {
out += base64encodechars.charAt(c1 >> 2);
out += base64encodechars.charAt((c1 & 0x3) << 4);
out += "==";
break;
}
c2 = str.charCodeAt(i++);
if (i == len) {
out += base64encodechars.charAt(c1 >> 2);
out += base64encodechars.charAt(((c1 & 0x3) << 4) | ((c2 & 0xf0) >> 4));
out += base64encodechars.charAt((c2 & 0xf) << 2);
out += "=";
break;
}
c3 = str.charCodeAt(i++);
out += base64encodechars.charAt(c1 >> 2);
out += base64encodechars.charAt(((c1 & 0x3) << 4) | ((c2 & 0xf0) >> 4));
out += base64encodechars.charAt(((c2 & 0xf) << 2) | ((c3 & 0xc0) >> 6));
out += base64encodechars.charAt(c3 & 0x3f);
}
return out;
}

function base64decode(str) {
var c1, c2, c3, c4;
var i, len, out;

len = str.length;

i = 0;
out = "";
while (i < len) {

do {
c1 = base64decodechars[str.charCodeAt(i++) & 0xff];
} while (i < len && c1 == -1);
if (c1 == -1)
break;

do {
c2 = base64decodechars[str.charCodeAt(i++) & 0xff];
} while (i < len && c2 == -1);
if (c2 == -1)
break;

out += String.fromCharCode((c1 << 2) | ((c2 & 0x30) >> 4));

do {
c3 = str.charCodeAt(i++) & 0xff;
if (c3 == 61)
return out;
c3 = base64decodechars[c3];
} while (i < len && c3 == -1);
if (c3 == -1)
break;

out += String.fromCharCode(((c2 & 0xf) << 4) | ((c3 & 0x3c) >> 2));

do {
c4 = str.charCodeAt(i++) & 0xff;
if (c4 == 61)
return out;
c4 = base64decodechars[c4];
} while (i < len && c4 == -1);
if (c4 == -1)
break;
out += String.fromCharCode(((c3 & 0x03) << 6) | c4);
}
return out;
}
</script>