WECHAT-UNIAPP/util/base64.js

export default class Base64 {  
   
  // private property  
  _keyStr = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=";  
  
  static getInstance(){
    if (!this.instance) {
      this.instance = new Base64();
    }
    return this.instance
  }
    
  // public method for encoding  
  encode = function (input) {  
      var output = "";  
      var chr1, chr2, chr3, enc1, enc2, enc3, enc4;  
      var i = 0;  
      input = this._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 +  
          this._keyStr.charAt(enc1) + this._keyStr.charAt(enc2) +  
          this._keyStr.charAt(enc3) + this._keyStr.charAt(enc4);  
      }  
      return output;  
  }  
 
  // public method for decoding  
  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 = this._keyStr.indexOf(input.charAt(i++));  
          enc2 = this._keyStr.indexOf(input.charAt(i++));  
          enc3 = this._keyStr.indexOf(input.charAt(i++));  
          enc4 = this._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 = this._utf8_decode(output);  
      return output;  
  }  
 
  // private method for UTF-8 encoding  
  _utf8_encode(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(utftext) {  

      let [string, i, c, c1, c2, c3] = ['', 0, 0, 0, 0, 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;  
  }  
}