React, ES6 – getInitialState was defined on a plain JavaScript class

• getInitialState is not used in ES6 classes. Instead assign this.state in the constructor.
• propTypes should be a static class variable or assigned to the class, it should not be assigned to component instances.
• Member methods are not “auto-bound” in ES6 classes. For methods used as callbacks, either use class property initializers or assign bound instances in the constructor.

export default class RadioOther extends React.Component {

  static propTypes = {
    name: React.PropTypes.string.isRequired,
  };

  constructor(props) {
    super(props);
    this.state = {
      otherChecked: false,
    };
  }

  // Class property initializer. `this` will be the instance when
  // the function is called.
  onRadChange = () => {
    ...
  };

  ...

}

See more in the React’s documentation about ES6 Classes: Converting a Function to a Class