Well if you are in strict mode, it should break the build with an error, not a warning. This seems to be a linting rule. But you see the issue with defaultProp

Well if you are in strict mode, it should break the build with an error, not a warning. This seems to be a linting rule. But you see the issue with defaultProps and state here. You can basically assign anything to defaultProps or use in setState() even so you were explicit of the props type in the Generic Type Argument.