src/polyfill/atob.js

// Copied from https://github.com/strophe/strophejs/blob/e06d027/src/polyfills.js#L149

// This code was written by Tyler Akins and has been placed in the
// public domain.  It would be nice if you left this header intact.
// Base64 code from Tyler Akins -- http://rumkin.com

#if !POLYFILL
#error "this file should never be included unless POLYFILL is set"
#endif

#if !ENVIRONMENT_MAY_BE_SHELL && !ENVIRONMENT_MAY_BE_NODE
#error "this polyfill should only be included when targetting node or shell"
#endif

if (typeof atob == 'undefined') {
  if (typeof global != 'undefined' && typeof globalThis == 'undefined') {
    globalThis = global;
  }

  /**
   * Decodes a base64 string.
   * @param {string} input The string to decode.
   */
  globalThis.atob = function(input) {
    var keyStr = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=';

    var output = '';
    var chr1, chr2, chr3;
    var enc1, enc2, enc3, enc4;
    var i = 0;
    // remove all characters that are not A-Z, a-z, 0-9, +, /, or =
    input = input.replace(/[^A-Za-z0-9\+\/\=]/g, '');
    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);
      }
    } while (i < input.length);
    return output;
  };
}