components.js

// old way
import React from 'react'
var App = React.createClass({ // ew, an object
  componentWillMount: function () {}, // ew, commas needed
  render: function() {
    return <div />
  }
})

// React 0.13 way
import React, { Component } from 'react'
class App extends Component {
  componentWillMount = () => {} // no commas needed. = () => needed for this binding
  render () {
    return <div />
  }
}

// Added in React 0.14: Stateless components. Only works if pure i.e. only uses props
import React from 'react'
const App = props => <div />
App.displayName = 'App' // Needed to show name in React Dev Tools

// Add export default to any of the above to export them
// 0.12 (two options)
export default App // preferred
export default React.createClass()

// 0.13 (two options)
export default class App extends Component {} // preferred
export default App

// 0.14 (two options)
export default App // preferred
export default props => <div />