When React was initially released, there was no idiomatic way to create classes in JavaScript, so we provided our own: React.createClass.
Later, classes were added to the language as part of ES2015, so we added the ability to create React components using JavaScript classes. Along with functional components, JavaScript classes are now the preferred way to create components in React.
For your existing createClass components, we recommend that you migrate them to JavaScript classes. However, if you have components that rely on mixins, converting to classes may not be immediately feasible. If so, create-react-class is available on npm as a drop-in replacement.
According to Facebook https://facebook.github.io/react/blog/2017/04/07/react-v15.5.0.html
Later, classes were added to the language as part of ES2015, so we added the ability to create React components using JavaScript classes. Along with functional components, JavaScript classes are now the preferred way to create components in React.
For your existing createClass components, we recommend that you migrate them to JavaScript classes. However, if you have components that rely on mixins, converting to classes may not be immediately feasible. If so, create-react-class is available on npm as a drop-in replacement.