If you write a bunch of ES6 classes, creator will bundle your classes with lots of duplicated babel helper functions in front of each compiled class:

var _createClass = (function() {
  function defineProperties(target, props) {
    for (var i = 0; i < props.length; i++) {
      var descriptor = props[i];
      descriptor.enumerable = descriptor.enumerable || false;
      descriptor.configurable = true;
      if ("value" in descriptor) descriptor.writable = true;
      Object.defineProperty(target, descriptor.key, descriptor);
    }
  }
  return function(Constructor, protoProps, staticProps) {
    if (protoProps) defineProperties(Constructor.prototype, protoProps);
    if (staticProps) defineProperties(Constructor, staticProps);
    return Constructor;
  };
})();

More info and possible solutions, refer to :

babel/babel#4709

https://stackoverflow.com/questions/38826550/duplicated-declarations-in-compiled-out-file-using-babel