In this video, we’ll add PropTypes to some of our existing components to ensure that each component gets the data it needs to function properly.
The lesson video has been updated!
If anyone else is having the error: "Uncaught TypeError: Cannot set property 'ReactFireMixin' of undefined" make sure to double check the webpack.config.js that was my problem lol
For those who learning in ES6 syntax, I believe the propTypes setting would be, for example in UserProfile component, type these lines right after class UserProfile component : UserProfile.propTypes = { username: React.PropTypes.string.isRequired, bio: React.PropTypes.object.isRequired }; It works for me :)