js實現base64編碼

function base64encode(str) {
str = utf16to8(str);
var out, i, len;
var c1, c2, c3;
var base64EncodeChars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
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;
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);
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);
}
out = utf8to16(out);
return out;
}
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:
out += str.charAt(i-1);
break;
case 12: case 13:
char2 = str.charCodeAt(i++);
out += String.fromCharCode(((c & 0x1F) << 6)|(char2 & 0x3F));
break;
case 14:
char2 = str.charCodeAt(i++);
char3 = str.charCodeAt(i++);
out += String.fromCharCode(((c & 0x0F) << 12)|((char2 & 0x3F) << 6)|((char3 & 0x3F) << 0));
break;
}
}
return out;
}