Es6 writing in react redux

  node.js, question

Recently, when studying react redux, I met some places I didn’t know when looking at the official examples of redux. I hope I can get help from everyone.
The following is an example from redux

const App = () => (
 <AddTodo />
 <VisibleTodoList />
 <Footer />
 export default App

The following is an example of react

var CommentBox = React.createClass({
 render: function() {
 return (
 <div className="commentBox">
 <CommentList />
 <CommentForm />

The two pieces of code I want to ask are components. I can understand the following writing method, but I don’t know the principle of the above writing method, or where there are documents to introduce this writing method.

I don’t know whether LZ doesn’t understand the arrow function of ES6 or the writing of this component in react. The former goes to tutorial while the latter goes to see the official documents.The last chapter