React Hook "useState" cannot be called in a class component. React Hooks must be called in a React function component or a custom React Hook function code example

Example 1: React Hook "useState" is called in function "app" which is neither a React function component or a custom React Hook function react-hooks/rules-of-hooks

//Try to capitalize 'app' like
const App = props => {...}

export default App;

Example 2: React Hook "useState" is called in function "app" which is neither a React function component or a custom React Hook function react-hooks/rules-of-hooks

capitalize 
const App