base64Decode

	function base64Decode(decodeStr){
		if(!decodeStr) return ;
		var base64IndexTable = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/';
		var BitPattern='',trueDecodeStr =decodeStr.substring(0,decodeStr.indexOf("=")), 
			blockNumber= decodeStr.substring(decodeStr.indexOf("=")).length,result='';
		for (var i = 0; i < trueDecodeStr.length; i++) {
			//得到每个base64字符的索引
			var base64Index =base64IndexTable.indexOf(trueDecodeStr[i]);
			var binaryStr = (base64Index).toString(2),newBinaryStr='',newBlockBinaryStr='';
			for (var j = 0; j < 6-binaryStr.length; j++) {
				newBinaryStr += '0';
			}
			binaryStr = newBinaryStr+binaryStr;
			BitPattern += binaryStr;
		}

		BitPattern =BitPattern.substring(0,BitPattern.length-2*blockNumber);

		for (var i = 0; i < BitPattern.length/8; i++) {
			var ASCIIChar = parseInt(BitPattern.substring(8*i,8*(i+1)),2);
				result += String.fromCharCode(ASCIIChar)
		}
		return result;
	}