Base64编码和解码实现

  1 function Base64() {
  2     // private property
  3     _keyStr = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=";
  4     // public method for encoding
  5     this.encode = function (input) {
  6         var output = "";
  7         var chr1, chr2, chr3, enc1, enc2, enc3, enc4;
  8         var i = 0;
  9         input = _utf8_encode(input);
 10         while (i < input.length) {
 11             chr1 = input.charCodeAt(i++);
 12             chr2 = input.charCodeAt(i++);
 13             chr3 = input.charCodeAt(i++);
 14             enc1 = chr1 >> 2;
 15             enc2 = ((chr1 & 3) << 4) | (chr2 >> 4);
 16             enc3 = ((chr2 & 15) << 2) | (chr3 >> 6);
 17             enc4 = chr3 & 63;
 18             if (isNaN(chr2)) {
 19                 enc3 = enc4 = 64;
 20             } else if (isNaN(chr3)) {
 21                 enc4 = 64;
 22             }
 23             output = output +
 24                     _keyStr.charAt(enc1) + _keyStr.charAt(enc2) +
 25                     _keyStr.charAt(enc3) + _keyStr.charAt(enc4);
 26         }
 27         return output;
 28     };
 29     // public method for decoding
 30     this.decode = function (input) {
 31         var output = "";
 32         var chr1, chr2, chr3;
 33         var enc1, enc2, enc3, enc4;
 34         var i = 0;
 35         input = input.replace(/[^A-Za-z0-9\+\/\=]/g, "");
 36         while (i < input.length) {
 37             enc1 = _keyStr.indexOf(input.charAt(i++));
 38             enc2 = _keyStr.indexOf(input.charAt(i++));
 39             enc3 = _keyStr.indexOf(input.charAt(i++));
 40             enc4 = _keyStr.indexOf(input.charAt(i++));
 41             chr1 = (enc1 << 2) | (enc2 >> 4);
 42             chr2 = ((enc2 & 15) << 4) | (enc3 >> 2);
 43             chr3 = ((enc3 & 3) << 6) | enc4;
 44             output = output + String.fromCharCode(chr1);
 45             if (enc3 != 64) {
 46                 output = output + String.fromCharCode(chr2);
 47             }
 48             if (enc4 != 64) {
 49                 output = output + String.fromCharCode(chr3);
 50             }
 51         }
 52         output = _utf8_decode(output);
 53         return output;
 54     };
 55     // private method for UTF-8 encoding
 56     _utf8_encode = function (string) {
 57         string = string.replace(/\r\n/g, "\n");
 58         var utftext = "";
 59         for (var n = 0; n < string.length; n++) {
 60             var c = string.charCodeAt(n);
 61             if (c < 128) {
 62                 utftext += String.fromCharCode(c);
 63             } else if ((c > 127) && (c < 2048)) {
 64                 utftext += String.fromCharCode((c >> 6) | 192);
 65                 utftext += String.fromCharCode((c & 63) | 128);
 66             } else {
 67                 utftext += String.fromCharCode((c >> 12) | 224);
 68                 utftext += String.fromCharCode(((c >> 6) & 63) | 128);
 69                 utftext += String.fromCharCode((c & 63) | 128);
 70             }
 71         }
 72         return utftext;
 73     };
 74     // private method for UTF-8 decoding
 75     _utf8_decode = function (utftext) {
 76         var string = "";
 77         var i = 0;
 78         var c = c1 = c2 = 0;
 79         while (i < utftext.length) {
 80             c = utftext.charCodeAt(i);
 81             if (c < 128) {
 82                 string += String.fromCharCode(c);
 83                 i++;
 84             } else if ((c > 191) && (c < 224)) {
 85                 c2 = utftext.charCodeAt(i + 1);
 86                 string += String.fromCharCode(((c & 31) << 6) | (c2 & 63));
 87                 i += 2;
 88             } else {
 89                 c2 = utftext.charCodeAt(i + 1);
 90                 c3 = utftext.charCodeAt(i + 2);
 91                 string += String.fromCharCode(((c & 15) << 12) | ((c2 & 63) << 6) | (c3 & 63));
 92                 i += 3;
 93             }
 94         }
 95         return string;
 96     }
 97 }
 98 
 99 //调用和示例显示
100 var base = new Base64();
101 var str = document.getElementById("p1").innerHTML;
102 str = base.decode(str);  //解码
103 document.getElementById("p1").innerHTML = str;