Js实现Base64编码与解码

base64是一种基于64个可打印字符来表示二进制数据的表示方法。由于2的6次方等于64，所以每6个比特为一个单元，对应某个可打印字符。

base64常用于在通常处理文本数据的场合，表示、传输、存储一些二进制数据。包括mime的email，email via mime, 在xml中存储复杂数据。

1.加密解密方法使用：

//1.加密 
var str = '124中文内容'; 
var base = new base64(); 
var result = base.encode(str); 
//document.write(result); 
//2.解密 
var result2 = base.decode(result); 
document.write(result2); 

2.加密、解密算法封装：

/** 
* 
* base64 encode / decode 
* 
* @author haitao.tu 
* @date  2010-04-26 
* @email [e-mail] 
* 
*/ 
function base64() { 
  
  // private property 
  _keystr = "abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyz0123456789+/="; 
  
  // public method for encoding 
  this.encode = function (input) { 
    var output = ""; 
    var chr1, chr2, chr3, enc1, enc2, enc3, enc4; 
    var i = 0; 
    input = _utf8_encode(input); 
    while (i < input.length) { 
      chr1 = input.charcodeat(i++); 
      chr2 = input.charcodeat(i++); 
      chr3 = input.charcodeat(i++); 
      enc1 = chr1 >> 2; 
      enc2 = ((chr1 & 3) << 4) | (chr2 >> 4); 
      enc3 = ((chr2 & 15) << 2) | (chr3 >> 6); 
      enc4 = chr3 & 63; 
      if (isnan(chr2)) { 
        enc3 = enc4 = 64; 
      } else if (isnan(chr3)) { 
        enc4 = 64; 
      } 
      output = output + 
      _keystr.charat(enc1) + _keystr.charat(enc2) + 
      _keystr.charat(enc3) + _keystr.charat(enc4); 
    } 
    return output; 
  } 
  
  // public method for decoding 
  this.decode = function (input) { 
    var output = ""; 
    var chr1, chr2, chr3; 
    var enc1, enc2, enc3, enc4; 
    var i = 0; 
    input = input.replace(/[^a-za-z0-9\+\/\=]/g, ""); 
    while (i < input.length) { 
      enc1 = _keystr.indexof(input.charat(i++)); 
      enc2 = _keystr.indexof(input.charat(i++)); 
      enc3 = _keystr.indexof(input.charat(i++)); 
      enc4 = _keystr.indexof(input.charat(i++)); 
      chr1 = (enc1 << 2) | (enc2 >> 4); 
      chr2 = ((enc2 & 15) << 4) | (enc3 >> 2); 
      chr3 = ((enc3 & 3) << 6) | enc4; 
      output = output + string.fromcharcode(chr1); 
      if (enc3 != 64) { 
        output = output + string.fromcharcode(chr2); 
      } 
      if (enc4 != 64) { 
        output = output + string.fromcharcode(chr3); 
      } 
    } 
    output = _utf8_decode(output); 
    return output; 
  } 
  
  // private method for utf-8 encoding 
  _utf8_encode = function (string) { 
    string = string.replace(/\r\n/g,"\n"); 
    var utftext = ""; 
    for (var n = 0; n < string.length; n++) { 
      var c = string.charcodeat(n); 
      if (c < 128) { 
        utftext += string.fromcharcode(c); 
      } else if((c > 127) && (c < 2048)) { 
        utftext += string.fromcharcode((c >> 6) | 192); 
        utftext += string.fromcharcode((c & 63) | 128); 
      } else { 
        utftext += string.fromcharcode((c >> 12) | 224); 
        utftext += string.fromcharcode(((c >> 6) & 63) | 128); 
        utftext += string.fromcharcode((c & 63) | 128); 
      } 
  
    } 
    return utftext; 
  } 
  
  // private method for utf-8 decoding 
  _utf8_decode = function (utftext) { 
    var string = ""; 
    var i = 0; 
    var c = c1 = c2 = 0; 
    while ( i < utftext.length ) { 
      c = utftext.charcodeat(i); 
      if (c < 128) { 
        string += string.fromcharcode(c); 
        i++; 
      } else if((c > 191) && (c < 224)) { 
        c2 = utftext.charcodeat(i+1); 
        string += string.fromcharcode(((c & 31) << 6) | (c2 & 63)); 
        i += 2; 
      } else { 
        c2 = utftext.charcodeat(i+1); 
        c3 = utftext.charcodeat(i+2); 
        string += string.fromcharcode(((c & 15) << 12) | ((c2 & 63) << 6) | (c3 & 63)); 
        i += 3; 
      } 
    } 
    return string; 
  } 
} 

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