where is the exports variable defined ?

consumer.es.js

export {Worker} from './package';

consumer.generated_code.js

"use strict";

exports.Worker = require("./package").Worker;
exports.__esModule = true;

// where is exports defined by 6to5 ?
// and no included method for require ?
// what is `__esModule` ? what is it used for ?

worker.es.js

export class Worker {
   constructor(name) {
      this._name = name;
   }

   get name() {
      return this._name;
   }

   doWork() {
      return `${this.name} is working`;
   }
}

worker.generated_code.js

"use strict";

var _prototypeProperties = function (child, staticProps, instanceProps) { if (staticProps) Object.defineProperties(child, staticProps); if (instanceProps) Object.defineProperties(child.prototype, instanceProps); };

var _classCallCheck = function (instance, Constructor) { if (!(instance instanceof Constructor)) { throw new TypeError("Cannot call a class as a function"); } };

var Worker = exports.Worker = (function () {
   function Worker(name) {
      _classCallCheck(this, Worker);

      this._name = name;
   }

   _prototypeProperties(Worker, null, {
      name: {
         get: function () {
            return this._name;
         },
         configurable: true
      },
      doWork: {
         value: function doWork() {
            return "" + this.name + " is working";
         },
         writable: true,
         configurable: true
      }
   });

   return Worker;
})();
exports.__esModule = true;

// output
// Can't find variable: exports

modules are not shown in http://kangax.github.io/compat-table/es6 yet
see compat-table/compat-table#316