React.Component is a generic type(aka React.Component<PropType, StateType>), so we want to provide it with (optional) prop and state type parameters:
type MyProps = {
// using `interface` is also ok
message: string;
};
type MyState = {
count: number; // like this
};
class App extends React.Component<MyProps, MyState> {
state: MyState = {
// optional second annotation for better type inference
count: 0,
};
render() {
return (
<div>
{this.props.message} {this.state.count}
</div>
);
}
}