Detailed explanation of JS implementation of Base64 encoding and decoding examples

Js implements Base64 encoding and decoding

Base64 is actually a simple substitution encryption method, but the purpose of BASE64 is often not to prevent information leakage, and in order to facilitate transmission, the information after BASE64 encoding will be longer than the original information. About 4/3 times.

Base64 is a representation method for binary data based on 64 printable characters. Since 2 to the 6th power is equal to 64, every 6 bits is a unit, corresponding to a printable character.

Base64 is often used to represent, transmit, and store some binary data in situations where text data is usually processed. Including MIME email, email via MIME, storing complex data in XML.

1. Encryption and decryption method use:

//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 packaging:

/**
*
* 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;
 }
}