Detailed code explanation for JavaScript implementation of Base64 encoding and decoding

This article shares with you a detailed code explanation of jJavaScript's implementation of Base64 encoding and decoding. The content is quite good. I hope it can help friends in need.

1. Encryption and decryption Method using

//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. Encryption and decryption algorithm encapsulation:

/**
*
* 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;
 }
}

Just introduce the encapsulation code and use it.

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