React-router v5.1 supports hooks style API which is called useParams to make path params more accessible. In order to use useParams easily, routing of App.ts|js should be changed as follows.

• <Switch> should be placed on top of <Route> components
• Page components should be defined as a children component of <Route>, not like <Route component={}>.

See: https://reacttraining.com/blog/react-router-v5-1/