微信小程序解码base64

atob代替方法

base64_decode (input) {
          
    // 解码，配合decodeURIComponent使用
    var base64EncodeChars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=";
    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 = base64EncodeChars.indexOf(input.charAt(i++));
        enc2 = base64EncodeChars.indexOf(input.charAt(i++));
        enc3 = base64EncodeChars.indexOf(input.charAt(i++));
        enc4 = base64EncodeChars.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);
        }
    }
    return this.utf8_decode(output);
},
utf8_decode (utftext) {
          
    // utf-8解码
  var string = ;
  let i = 0;
  let c = 0;
  let c1 = 0;
  let c2 = 0;
  while (i < utftext.length) {
          
   
      c = utftext.charCodeAt(i);
      if (c < 128) {
          
   
          string += String.fromCharCode(c);
          i++;
      } else if ((c > 191) && (c < 224)) {
          
   
          c1 = utftext.charCodeAt(i + 1);
          string += String.fromCharCode(((c & 31) << 6) | (c1 & 63));
          i += 2;
      } else {
          
   
          c1 = utftext.charCodeAt(i + 1);
          c2 = utftext.charCodeAt(i + 2);
          string += String.fromCharCode(((c & 15) << 12) | ((c1 & 63) << 6) | (c2 & 63));
          i += 3;
      }
  }
  return string;
},