Unable to access this with babel converted

Question

I'm using es6 features and compile it with babel on nodeJs, but it seems that i'm unable to access to instance from another method

export default class TimeRouter {
  router : Router;
  path : string;

constructor(path:string='/api/v1/timerouter'){
  this.router = Router();
  this.path = path;

  this.init();

  this.timeRanges = {
   'LAST_SEMESTER' : 6, //nb of months,
   'LAST_12_MONTHS' : 12,
   'LAST_TRIMESTER' : 4,
   'LAST_YEAR' : 12 
  }

 }


 getTimeRanges(req: $Request, res:$Response): void {


  console.log('Test ranges',this); //returns undefined

  res.status(200).json(this.timeRanges);
 }


 init():void {
  this.router.get('/',this.getTimeRanges)
 }
}

With gulp-sourcemaps and gulp-babel, I get this gulp config :

    gulp.task('scripts', () => {
      return gulp.src('src/**/*.js')
      .pipe(sourcemaps.init())
      .pipe(babel())
      .pipe(sourcemaps.write('.'))
      .pipe(gulp.dest('build'));
    });

It renders something like this :

    'use strict';

    Object.defineProperty(exports, "__esModule", {
      value: true
    });

    var _createClass = function () { function defineProperties(target, props) { for (var i = 0; i  0 && arguments[0] !== undefined ? arguments[0] : '/api/v1/timerouter';

        _classCallCheck(this, TimeRouter);

        this.router = (0, _express.Router)();
        this.path = path;

        this.init();

        this.timeRanges = {
          'LAST_SEMESTER': 6, //nb of months,
          'LAST_12_MONTHS': 12,
          'LAST_TRIMESTER': 4,
          'LAST_YEAR': 12
        };
      }

      _createClass(TimeRouter, [{
        key: 'getTimeRanges',
        value: function getTimeRanges(req, res) {
          console.log(this.timeRanges);
          var ranges = this.timeRanges;

          res.status(200).json(ranges);
        }
      }, {
        key: 'init',
        value: function init() {
          this.router.get('/', this.getTimeRanges);
        }
      }]);

      return TimeRouter;
    }();

    exports.default = TimeRouter;
    //# sourceMappingURL=TimeRouter.js.map

Any ideas why I can't access to the current instance ?