提供一種Base64編碼,並輸出UTF-8格式的BASE64編碼方式。本程式在微信小程式開發工具中已經測試通過。

 Base64程式碼：

(function(){
	var BASE64_MAPPING = [
		'A','B','C','D','E','F','G','H',
		'I','J','K','L','M','N','O','P',
		'Q','R','S','T','U','V','W','X',
		'Y','Z','a','b','c','d','e','f',
		'g','h','i','j','k','l','m','n',
		'o','p','q','r','s','t','u','v',
		'w','x','y','z','0','1','2','3',
		'4','5','6','7','8','9','+','/'
	];

	/**
	 *ascii convert to binary
	 */
	var _toBinary = function(ascii){
		var binary = new Array();
		while(ascii > 0){
			var b = ascii%2;
			ascii = Math.floor(ascii/2);
			binary.push(b);
		}
		/*
		var len = binary.length;
		if(6-len > 0){
			for(var i = 6-len ; i > 0 ; --i){
				binary.push(0);
			}
		}*/
		binary.reverse();
		return binary;
	};

	/**
	 *binary convert to decimal
	 */
	var _toDecimal  = function(binary){
		var dec = 0;
		var p = 0;
		for(var i = binary.length-1 ; i >= 0 ; --i){
			var b = binary[i];
			if(b == 1){
				dec += Math.pow(2 , p);
			}
			++p;
		}
		return dec;
	};

	/**
	 *unicode convert to utf-8
	 */
	var _toUTF8Binary = function(c , binaryArray){
		var mustLen = (8-(c+1)) + ((c-1)*6);
		var fatLen = binaryArray.length;
		var diff = mustLen - fatLen;
		while(--diff >= 0){
			binaryArray.unshift(0);
		}
		var binary = [];
		var _c = c;
		while(--_c >= 0){
			binary.push(1);
		}
		binary.push(0);
		var i = 0 , len = 8 - (c+1);
		for(; i < len ; ++i){
			binary.push(binaryArray[i]);
		}

		for(var j = 0 ; j < c-1 ; ++j){
			binary.push(1);
			binary.push(0);
			var sum = 6;
			while(--sum >= 0){
				binary.push(binaryArray[i++]);
			}
		}
		return binary;
	};

	var __BASE64 = {
			/**
			 *BASE64 Encode
			 */
			encoder:function(str){
				var base64_Index = [];
				var binaryArray = [];
				for(var i = 0 , len = str.length ; i < len ; ++i){
					var unicode = str.charCodeAt(i);
					var _tmpBinary = _toBinary(unicode);
					if(unicode < 0x80){
						var _tmpdiff = 8 - _tmpBinary.length;
						while(--_tmpdiff >= 0){
							_tmpBinary.unshift(0);
						}
						binaryArray = binaryArray.concat(_tmpBinary);
					}else if(unicode >= 0x80 && unicode <= 0x7FF){
						binaryArray = binaryArray.concat(_toUTF8Binary(2 , _tmpBinary));
					}else if(unicode >= 0x800 && unicode <= 0xFFFF){//UTF-8 3byte
						binaryArray = binaryArray.concat(_toUTF8Binary(3 , _tmpBinary));
					}else if(unicode >= 0x10000 && unicode <= 0x1FFFFF){//UTF-8 4byte
						binaryArray = binaryArray.concat(_toUTF8Binary(4 , _tmpBinary));	
					}else if(unicode >= 0x200000 && unicode <= 0x3FFFFFF){//UTF-8 5byte
						binaryArray = binaryArray.concat(_toUTF8Binary(5 , _tmpBinary));
					}else if(unicode >= 4000000 && unicode <= 0x7FFFFFFF){//UTF-8 6byte
						binaryArray = binaryArray.concat(_toUTF8Binary(6 , _tmpBinary));
					}
				}

				var extra_Zero_Count = 0;
				for(var i = 0 , len = binaryArray.length ; i < len ; i+=6){
					var diff = (i+6)-len;
					if(diff == 2){
						extra_Zero_Count = 2;
					}else if(diff == 4){
						extra_Zero_Count = 4;
					}
					//if(extra_Zero_Count > 0){
					//	len += extra_Zero_Count+1;
					//}
					var _tmpExtra_Zero_Count = extra_Zero_Count;
					while(--_tmpExtra_Zero_Count >= 0){
						binaryArray.push(0);
					}
					base64_Index.push(_toDecimal(binaryArray.slice(i , i+6)));
				}

				var base64 = '';
				for(var i = 0 , len = base64_Index.length ; i < len ; ++i){
					base64 += BASE64_MAPPING[base64_Index[i]];
				}

				for(var i = 0 , len = extra_Zero_Count/2 ; i < len ; ++i){
					base64 += '=';
				}
				return base64;
			},
			/**
			 *BASE64  Decode for UTF-8 
			 */
			decoder : function(_base64Str){
				var _len = _base64Str.length;
				var extra_Zero_Count = 0;
				/**
				 *計算在進行BASE64編碼的時候，補了幾個0
				 */
				if(_base64Str.charAt(_len-1) == '='){
					//alert(_base64Str.charAt(_len-1));
					//alert(_base64Str.charAt(_len-2));
					if(_base64Str.charAt(_len-2) == '='){//兩個等號說明補了4個0
						extra_Zero_Count = 4;
						_base64Str = _base64Str.substring(0 , _len-2);
					}else{//一個等號說明補了2個0
						extra_Zero_Count = 2;
						_base64Str = _base64Str.substring(0 , _len - 1);
					}
				}

				var binaryArray = [];
				for(var i = 0 , len = _base64Str.length; i < len ; ++i){
					var c = _base64Str.charAt(i);
					for(var j = 0 , size = BASE64_MAPPING.length ; j < size ; ++j){
						if(c == BASE64_MAPPING[j]){
							var _tmp = _toBinary(j);
							/*不足6位的補0*/
							var _tmpLen = _tmp.length;
							if(6-_tmpLen > 0){
								for(var k = 6-_tmpLen ; k > 0 ; --k){
									_tmp.unshift(0);
								}
							}
							binaryArray = binaryArray.concat(_tmp);
							break;
						}
					}
				}

				if(extra_Zero_Count > 0){
					binaryArray = binaryArray.slice(0 , binaryArray.length - extra_Zero_Count);
				}

				var unicode = [];
				var unicodeBinary = [];
				for(var i = 0 , len = binaryArray.length ; i < len ; ){
					if(binaryArray[i] == 0){
						unicode=unicode.concat(_toDecimal(binaryArray.slice(i,i+8)));
						i += 8;
					}else{
						var sum = 0;
						while(i < len){
							if(binaryArray[i] == 1){
								++sum;
							}else{
								break;
							}
							++i;
						}
						unicodeBinary = unicodeBinary.concat(binaryArray.slice(i+1 , i+8-sum));
						i += 8 - sum;
						while(sum > 1){
							unicodeBinary = unicodeBinary.concat(binaryArray.slice(i+2 , i+8));
							i += 8;
							--sum;
						}
						unicode = unicode.concat(_toDecimal(unicodeBinary));
						unicodeBinary = [];
					}
				}
				return unicode;
			}
	};

  //window.BASE64 = __BASE64;
  module.exports = {
    CusBASE64: __BASE64
  }
})();
 

   呼叫方式：

//檔案引用
var CusBase64 = require('base64.js');
//函式呼叫
var result=CusBase64.CusBASE64.encoder(data);