用js編解碼base64

編碼規則

Base64編碼的思想是是采用64個基本的ASCII碼字元對資料進行重新編碼。它将需要編碼的資料拆分成位元組數組。以3個位元組為一組。按順序排列24 位資料，再把這24位資料分成4組，即每組6位。再在每組的的最高位前補兩個0湊足一個位元組。這樣就把一個3位元組為一組的資料重新編碼成了4個位元組。當所要編碼的資料的位元組數不是3的整倍數，也就是說在分組時最後一組不夠3個位元組。這時在最後一組填充1到2個0位元組。并在最後編碼完成後在結尾添加1到2個 “=”。

實作的代碼：

1:  //下面是64個基本的編碼      

2:  var base64EncodeChars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";      

3:  var base64DecodeChars = new Array(      

4:      -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,      

5:      -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,      

6:      -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 62, -1, -1, -1, 63,      

7:      52, 53, 54, 55, 56, 57, 58, 59, 60, 61, -1, -1, -1, -1, -1, -1,      

8:      -1,  0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 12, 13, 14,      

9:      15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, -1, -1, -1, -1, -1,      

10:      -1, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40,      

11:      41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, -1, -1, -1, -1, -1);      

12:  //編碼的方法      

13:  function base64encode(str) {      

14:      var out, i, len;      

15:      var c1, c2, c3;      

16:      len = str.length;      

17:      i = 0;      

18:      out = "";      

19:      while(i < len) {      

20:      c1 = str.charCodeAt(i++) & 0xff;      

21:      if(i == len)      

22:      {      

23:          out += base64EncodeChars.charAt(c1 >> 2);      

24:          out += base64EncodeChars.charAt((c1 & 0x3) << 4);      

25:          out += "==";      

26:          break;      

27:      }      

28:      c2 = str.charCodeAt(i++);      

29:      if(i == len)      

30:      {      

31:          out += base64EncodeChars.charAt(c1 >> 2);      

32:          out += base64EncodeChars.charAt(((c1 & 0x3)<< 4) | ((c2 & 0xF0) >> 4));      

33:          out += base64EncodeChars.charAt((c2 & 0xF) << 2);      

34:          out += "=";      

35:          break;      

36:      }      

37:      c3 = str.charCodeAt(i++);      

38:      out += base64EncodeChars.charAt(c1 >> 2);      

39:      out += base64EncodeChars.charAt(((c1 & 0x3)<< 4) | ((c2 & 0xF0) >> 4));      

40:      out += base64EncodeChars.charAt(((c2 & 0xF) << 2) | ((c3 & 0xC0) >>6));      

41:      out += base64EncodeChars.charAt(c3 & 0x3F);      

42:      }      

43:      return out;      

44:  }      

45:  //解碼的方法      

46:  function base64decode(str) {      

47:      var c1, c2, c3, c4;      

48:      var i, len, out;      

49:      len = str.length;      

50:      i = 0;      

51:      out = "";      

52:      while(i < len) {      

54:      do {      

55:          c1 = base64DecodeChars[str.charCodeAt(i++) & 0xff];      

56:      } while(i < len && c1 == -1);      

57:      if(c1 == -1)      

58:          break;      

60:      do {      

61:          c2 = base64DecodeChars[str.charCodeAt(i++) & 0xff];      

62:      } while(i < len && c2 == -1);      

63:      if(c2 == -1)      

64:          break;      

65:      out += String.fromCharCode((c1 << 2) | ((c2 & 0x30) >> 4));      

67:      do {      

68:          c3 = str.charCodeAt(i++) & 0xff;      

69:          if(c3 == 61)      

70:          return out;      

71:          c3 = base64DecodeChars[c3];      

72:      } while(i < len && c3 == -1);      

73:      if(c3 == -1)      

74:          break;      

75:      out += String.fromCharCode(((c2 & 0XF) << 4) | ((c3 & 0x3C) >> 2));      

77:      do {      

78:          c4 = str.charCodeAt(i++) & 0xff;      

79:          if(c4 == 61)      

80:          return out;      

81:          c4 = base64DecodeChars[c4];      

82:      } while(i < len && c4 == -1);      

83:      if(c4 == -1)      

84:          break;      

85:      out += String.fromCharCode(((c3 & 0x03) << 6) | c4);      

86:      }      

87:      return out;      

88:  }      

89:  function utf16to8(str) {      

90:      var out, i, len, c;      

91:      out = "";      

92:      len = str.length;      

93:      for(i = 0; i < len; i++) {      

94:      c = str.charCodeAt(i);      

95:      if ((c >= 0x0001) && (c <= 0x007F)) {      

96:          out += str.charAt(i);      

97:      } else if (c > 0x07FF) {      

98:          out += String.fromCharCode(0xE0 | ((c >> 12) & 0x0F));      

99:          out += String.fromCharCode(0x80 | ((c >>  6) & 0x3F));      

100:          out += String.fromCharCode(0x80 | ((c >>  0) & 0x3F));      

101:      } else {      

102:          out += String.fromCharCode(0xC0 | ((c >>  6) & 0x1F));      

103:          out += String.fromCharCode(0x80 | ((c >>  0) & 0x3F));      

104:      }      

105:      }      

106:      return out;      

107:  }      

108:  function utf8to16(str) {      

109:      var out, i, len, c;      

110:      var char2, char3;      

111:      out = "";      

112:      len = str.length;      

113:      i = 0;      

114:      while(i < len) {      

115:      c = str.charCodeAt(i++);      

116:      switch(c >> 4)      

117:      {       

118:        case 0: case 1: case 2: case 3: case 4: case 5: case 6: case 7:      

119:          // 0xxxxxxx      

120:          out += str.charAt(i-1);      

121:          break;      

122:        case 12: case 13:      

123:          // 110x xxxx   10xx xxxx      

124:          char2 = str.charCodeAt(i++);      

125:          out += String.fromCharCode(((c & 0x1F) << 6) | (char2 & 0x3F));      

126:          break;      

127:        case 14:      

128:          // 1110 xxxx  10xx xxxx  10xx xxxx      

129:          char2 = str.charCodeAt(i++);      

130:          char3 = str.charCodeAt(i++);      

131:          out += String.fromCharCode(((c & 0x0F) << 12) |      

132:                         ((char2 & 0x3F) << 6) |      

133:                         ((char3 & 0x3F) << 0));      

134:          break;      

135:      }      

136:      }      

137:      return out;      

138:  }      

調用：      

1:  //編碼      

2:  value = base64encode(utf16to8(src))      

3:         

4:  //解碼      

5:  value = utf8to16(base64decode(src))      

轉載于:https://www.cnblogs.com/ricksun/archive/2012/08/27/2658654.html