I came across a couple of useful tricks when creating React components using the ES6 class syntax today - take a look at this example:

import React from 'react';

export default class Form extends React.Component {
	// declare default state - doesn't need to be in constructor
	// ES6+ only - property initialisers
	state = {
		hasChanged: false
	};

	constructor() {
		super();
	}

	// arrow function binds 'this' so it can be called from event
	// otherwise you'd need to have `this.formChanged = this.formChanged.bind(this)`
	// in constructor (otherwise `this.setState` doesn't exist)
	formChanged = () => this.setState({ hasChanged: true })

	render() {
		return (
			<form onChange={ this.formChanged }>
				<label>hello
				<input type="text" />
			</form>
		);
	}
}

export default

you can choose to export multiple things (functions, classes, variables etc) from ES6 classes, but one must be default so the compiler knows what to do with `import`. More on this here.

class Form extends React.Component

you can extend React.Component as a class, rather than use the React.createClass function.

Class properties

state = {
	hasChanged: false
};

State can be a class property, so you don't have to have this.state = {} in the constructor. This is an ES7 feature, so you'll need to include stage-0 in Babel, but is much more convenient than writing a lot of boilerplate.

Arrow functions

formChanged = () => this.setState({ hasChanged: true }) is an arrow function since it saves more boilerplate by binding this. Otherwise, this would need a function declaration as well as a line in the constructor to bind this, since the function is called from an event (so the context would be window, which doesn't have the setState function).

More reading

Using ES6+ features in Babel

Binding methods in React components