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 tuhaitao@foxmail.com
*
*/
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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