.babelrc

{
  "presets": [ "es2015-rollup" ],
  "plugins": ["transform-class-properties"]
}

out.js

(function (global, factory) {
  typeof exports === 'object' && typeof module !== 'undefined' ? factory() :
  typeof define === 'function' && define.amd ? define(factory) :
  (factory());
}(this, (function () { 'use strict';

var asyncGenerator = function () {
  function AwaitValue(value) {
    this.value = value;
  }

  function AsyncGenerator(gen) {
    var front, back;

    function send(key, arg) {
      return new Promise(function (resolve, reject) {
        var request = {
          key: key,
          arg: arg,
          resolve: resolve,
          reject: reject,
          next: null
        };

        if (back) {
          back = back.next = request;
        } else {
          front = back = request;
          resume(key, arg);
        }
      });
    }

    function resume(key, arg) {
      try {
        var result = gen[key](arg);
        var value = result.value;

        if (value instanceof AwaitValue) {
          Promise.resolve(value.value).then(function (arg) {
            resume("next", arg);
          }, function (arg) {
            resume("throw", arg);
          });
        } else {
          settle(result.done ? "return" : "normal", result.value);
        }
      } catch (err) {
        settle("throw", err);
      }
    }

    function settle(type, value) {
      switch (type) {
        case "return":
          front.resolve({
            value: value,
            done: true
          });
          break;

        case "throw":
          front.reject(value);
          break;

        default:
          front.resolve({
            value: value,
            done: false
          });
          break;
      }

      front = front.next;

      if (front) {
        resume(front.key, front.arg);
      } else {
        back = null;
      }
    }

    this._invoke = send;

    if (typeof gen.return !== "function") {
      this.return = undefined;
    }
  }

  if (typeof Symbol === "function" && Symbol.asyncIterator) {
    AsyncGenerator.prototype[Symbol.asyncIterator] = function () {
      return this;
    };
  }

  AsyncGenerator.prototype.next = function (arg) {
    return this._invoke("next", arg);
  };

  AsyncGenerator.prototype.throw = function (arg) {
    return this._invoke("throw", arg);
  };

  AsyncGenerator.prototype.return = function (arg) {
    return this._invoke("return", arg);
  };

  return {
    wrap: function (fn) {
      return function () {
        return new AsyncGenerator(fn.apply(this, arguments));
      };
    },
    await: function (value) {
      return new AwaitValue(value);
    }
  };
}();















var get = function get(object, property, receiver) {
  if (object === null) object = Function.prototype;
  var desc = Object.getOwnPropertyDescriptor(object, property);

  if (desc === undefined) {
    var parent = Object.getPrototypeOf(object);

    if (parent === null) {
      return undefined;
    } else {
      return get(parent, property, receiver);
    }
  } else if ("value" in desc) {
    return desc.value;
  } else {
    var getter = desc.get;

    if (getter === undefined) {
      return undefined;
    }

    return getter.call(receiver);
  }
};

















var set = function set(object, property, value, receiver) {
  var desc = Object.getOwnPropertyDescriptor(object, property);

  if (desc === undefined) {
    var parent = Object.getPrototypeOf(object);

    if (parent !== null) {
      set(parent, property, value, receiver);
    }
  } else if ("value" in desc && desc.writable) {
    desc.value = value;
  } else {
    var setter = desc.set;

    if (setter !== undefined) {
      setter.call(receiver, value);
    }
  }

  return value;
};

})));

package.json

{
  "name": "studyjs",
  "version": "1.1.2",
  "author": "Jacob Kelley <[email protected]>",
  "homepage": "https://github.com/dollarshaveclub/study",
  "description": "A client side A/B tester",
  "license": "MIT",
  "main": "./index.js",
  "repository": {
    "type": "git",
    "url": "git://github.com/dollarshaveclub/study.git"
  },
  "scripts": {
    "build": "./node_modules/gulp/bin/gulp.js build",
    "build-watch": "./node_modules/gulp/bin/gulp.js build-watch",
    "test": "./node_modules/mocha-phantomjs/bin/mocha-phantomjs --reporter spec test/runner.html",
    "pages": "git push -f origin master:gh-pages",
    "postpublish": "git tag $npm_package_version && git push origin --tags"
  },
  "devDependencies": {
    "babel-plugin-transform-class-properties": "^6.18.0",
    "babel-preset-es2015-rollup": "^1.1.1",
    "babel-preset-es2015": "6.9.0",
    "rollup-plugin-babel": "^2.6.1",
    "rollup-plugin-uglify": "^1.0.1",
    "rollup-stream": "^1.11.0",
    "vinyl-source-stream": "^1.1.0"
  }
}

source.js

class Foo {}