Javascript语言进行Base64编码

首先，假定网页的编码是utf-8，我们希望对于同样的字符串，用PHP和Javascript可以得到同样的Base64编码。

这里就会产生一个问题。因为Javascript内部的字符串，都以utf-16的形式进行保存，因此编码的时候，我们首先必须将utf-8的值转成utf-16再编码，解码的时候，则是解码后还需要将utf-16的值转回成utf-8。

网上已经有人写好了现成的Javascript函数：

/* utf.js - UTF-8 <=> UTF-16 convertion** Copyright (C) 1999 Masanao Izumo <[e-mail]>* Version: 1.0* LastModified: Dec 25 1999* This library is free. You can redistribute it and/or modify it.*//** Interfaces:* utf8 = utf16to8(utf16);* utf16 = utf8to16(utf8);*/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:// 0xxxxxxxout += str.charAt(i-1);break;case 12: case 13:// 110x xxxx 10xx xxxxchar2 = str.charCodeAt(i++);out += String.fromCharCode(((c & 0x1F) << 6) | (char2 & 0x3F));break;case 14:// 1110 xxxx 10xx xxxx 10xx xxxxchar2 = str.charCodeAt(i++);char3 = str.charCodeAt(i++);out += String.fromCharCode(((c & 0x0F) << 12) |((char2 & 0x3F) << 6) |((char3 & 0x3F) << 0));break;}}return out;}

上面的这段代码中定义了两个函数，utf16to8()用于将utf-16转成utf-8，utf8to16用于将utf-8转成utf-16。

下面才是真正用于base64编码的函数。

/* Copyright (C) 1999 Masanao Izumo <[e-mail]>* Version: 1.0* LastModified: Dec 25 1999* This library is free. You can redistribute it and/or modify it.*//** Interfaces:* b64 = base64encode(data);* data = base64decode(b64);*/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) {/* c1 */do {c1 = base64DecodeChars[str.charCodeAt(i++) & 0xff];} while(i < len && c1 == -1);if(c1 == -1)break;/* c2 */do {c2 = base64DecodeChars[str.charCodeAt(i++) & 0xff];} while(i < len && c2 == -1);if(c2 == -1)break;out += String.fromCharCode((c1 << 2) | ((c2 & 0x30) >> 4));/* c3 */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));/* c4 */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;}

上面代码中的base64encode()用于编码，base64decode()用于解码。

因此，对utf-8字符进行编码要这样写：

sEncoded=base64encode(utf16to8(str));

然后，解码要这样写：

sDecoded=utf8to16(base64decode(sEncoded));