【原创】Javascript版本Base64在线编码、解码。

<!doctype html><html><head>
<title>Base64 在线编码解码</title>
<script type="text/javascript">
onload = function()
{
	self.b64 = new Base64;
	self.sb = document.getElementById("source");
	self.tg = document.getElementById("target");
	self.utf = document.getElementById("useUTF");
	self.tm = document.getElementById("timer");
}
function Base64()
{
	var me = this;
	me.UseUTF = true;
	me.ZeroChar = 32;	// 解码时字符\x00转换成\x20（空格）以便显示
	var dic64 = new Object;
	var str64 = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
	for(var i = 0; i <str64.length; i++) dic64[str64.charAt(i)] = i;
	me.Encode = function(str)
	{
		str = GetCode(str);
		var arr = new Array;
		for(var i = 0; i < str.length; i++)
		{
			var s = str.charCodeAt(i).toString(2);
			while(s.length < 8) s = "0" + s;
			arr.push(s);
		}
		str = arr.join("");
		arr.length = 0;
		for(var i = 0; i < str.length; i+=6)
		{
			var s = str.substr(i, 6);
			while(s.length < 6) s += "0";
			arr.push(str64.charAt(parseInt(s, 2).toString(10)));
		}
		str = arr.join("");
		while(str.length % 4) str += "=";
		return str;
	}
	me.Decode = function(str)
	{
		var arr = new Array;
		str = str.replace(/[^A-Za-z0-9\+\/]/g, "");
		for(var i = 0; i < str.length; i++)
		{
			nmb = dic64[str.charAt(i)].toString(2);
			while(nmb.length < 6) nmb = "0" + nmb;
			arr.push(nmb);
		}
		str = arr.join("");
		arr.length = 0;
		for(var i = 0; i < str.length; i += 8)
		{
			var s = str.substr(i, 8);
			if(s.length < 8) break;
			arr.push(String.fromCharCode(parseInt(s, 2) || me.ZeroChar));
		}
		str = arr.join("");
		return me.UseUTF ? decodeURIComponent(escape(str)) : str;
	}
	function GetCode(str)
	{
		if(me.UseUTF) return unescape(encodeURI(str));
		str = escape(str).replace(/%u([A-F0-9]{2})([A-F0-9]{2})/g, "%$1%$2");
		return unescape(str);
	}
}
function toggle()
{
	sb.value = tg.value;
	tg.value = "";
}
function encode(isDecode)
{
	var date = new Date;
	b64.UseUTF = utf.checked; try{
	tg.value = b64[(isDecode ? "De" : "En") + "code"](sb.value);
	}catch(err){ tg.value = err.message; }
	tm.innerHTML = new Date - date;
}
function $(id){ return document.getElementById(id); }
</script></head><body>
请输入转换内容：
<div><textarea id="source" cols="65" rows="12"></textarea></div>
转换结果如下：<input type="button" value="上移" onclick="toggle()" />
<div><textarea id="target" readonly="true" cols="65" rows="12"></textarea></div>
<label><input type="checkbox" id="useUTF" checked="true" />使用UTF-8编码</label>
<input type="button" value="编码" onclick="encode(0)" />
<input type="button" value="解码" onclick="encode(1)" />
耗时 <tt id="timer">0</tt> ms
</body></html>

[您可以先修改代码再运行]

编码原理：
1、取每个字符的二进制值，例如“ABCD”对应的十进制为：[65, 66, 67, 68]，二进制为（8位）：[01000001, 01000010, 01000011, 01000100]。
2、将二进制每隔6位重新分隔为[010000, 010100, 001001, 000011, 010001, 00]，发现最后一组只有两位，我们在最后一组二进制数的后面补0，补充到6位为止，例如00补充为000000，01则应补充为010000。
3、将6位的二进制数转为10进制数，变为：[16, 20, 9, 3, 17, 0]，即为Base64的字典索引值。
4、查阅Base64字典，分别对应“QUJDRA”，长度不可被4整除，补充“=”后最终结果为“QUJDRA==”

Base64解码就是Base64编码的逆过程，这里就不再多说了。
Base64字典：ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/