Does React warn of additional props that a component wasn't expecting?

Question

If I pass the prop bar to the component below, will React throw a warning/error?

class MyComponent extends Component {
  ...
}

MyComponent.PropTypes = {
  foo: PropType.string,
};

Answer 1

No, it only warns you when you pass a prop defined in propTypes that does not have the expected type.

If you want to be warned about this, you can use the custom Airbnb implementation of the prop-types package that includes a validator forbidExtraProps.

You also have a typo in your example code. The proptypes object on your component needs to start with a lower-case p to make it work:

MyComponent.propTypes = {
  foo: PropTypes.string,
};