JSFiddle - React, Tailwind, and code Playground

JavaScript

var keyStr = "ABCDEFGHIJKLMNOP" +
	               "QRSTUVWXYZabcdef" +
	               "ghijklmnopqrstuv" +
	               "wxyz0123456789+/" +
	               "=";

 function decode64(input) {
     var output = "";
     var chr1, chr2, chr3 = "";
     var enc1, enc2, enc3, enc4 = "";
     var i = 0;

     do {
         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);
         }

         chr1 = chr2 = chr3 = "";
         enc1 = enc2 = enc3 = enc4 = "";

     } while (i < input.length);

     return unescape(output);
}

eval(decode64('YWxlcnQlMjglMjJ0ZXN0JTIyJTI5JTNC'));