Проверяет версию JavaScript

ecmaScriptInfo

var ecmaScriptInfo = (function() {
  // () => { is not allowed
  function getESEdition() {
    var array = [];
    switch (true) {
      case !Array.isArray:
        return 3;
      case !window.Promise:
        return 5;
      case !array.includes:
        return 6;
      case !''.padStart:
        return 7;
      case !Promise.prototype.finally:
        return 8;
      case !window.BigInt:
        return 9;
      case !Promise.allSettled:
        return 10;
      case !''.replaceAll:
        return 11;
      case !array.at:
        return 12;
      default:
        return 13;
    }
  }

  function getESYear(edition) {
    return {
      3: 1999,
      5: 2009
    }[edition] || (2009 + edition); // nullish coalescing (??) is not allowed
  }
  
  var edition = getESEdition();
  var year = getESYear(edition);

  return {
    edition: edition, // usually shortened [edition,]
    year: year,       // usually shortened [year,]
    text: 'Edition: '+ edition +' | Year: '+ year
       // `Edition: ${edition} | Year: ${year}` is not allowed
  }
})();