What are the differences between React’s createClass and ES6 class components?

In the earlier days of React, defining components using the `createClass` method was the norm. As JavaScript evolved and the ES6 (ECMAScript 2015) specification introduced class syntax, React adapted by offering the ability to define components as ES6 classes. These two methods bring about a few noteworthy differences:

1. Syntax & Structure: The most evident difference is in the syntax. With `createClass`, components are defined using a plain object, whereas ES6 class components use the class syntax, extending `React.Component`.

2. Auto-binding: In `createClass`, all methods are automatically bound to the component’s instance, meaning you could directly use `this` inside methods to refer to the component. With ES6 classes, this isn’t the case. Methods are not bound by default, often necessitating manual binding in the constructor or the use of arrow functions to retain the correct context for `this`.

3. Mixins: One of the features `createClass` supported was mixins, allowing the sharing of functionalities between multiple components. ES6 classes don’t natively support mixins. Instead, the React community has gravitated towards higher-order components (HOCs) and hooks to share logic across components.

4. PropTypes and DefaultProps: In `createClass`, `propTypes` and `getDefaultProps` were specified as object properties. With ES6 classes, `propTypes` and `defaultProps` are defined as static properties on the class.

5. Lifecycle Methods: While both approaches support lifecycle methods, such as `componentDidMount` or `shouldComponentUpdate`, the way they’re defined varies slightly in terms of syntax. ES6 class methods are cleaner, with fewer boilerplate codes around them.

6. Future of React: It’s crucial to note that the React team has indicated a shift away from `createClass`. With the introduction of hooks and function components becoming more prominent, ES6 class components remain a recommended way over `createClass` for those not yet adopting hooks.

While `createClass` provided a foundational approach to building components in early React, the evolution of JavaScript and React’s own capabilities have made ES6 class components and, more recently, function components with hooks, more favorable for developing modern React applications.