I just got a mystery react error after coding along with a tutorial. That’s pretty common, but it was pretty hard for me to figure out what the error was talking about from the message. Cutting to the chase (and so I can look it up easily next time) you get an “Super expression must either be null or a function, not undefined” error if you type

class xxxx extends React.component {}

as opposed to

class xxxx extends React.Component {}

The difference is in the capital C. Don’t make my mistake, or if you do then you can fix it quickly!