This is a example application of a todo app.
npm install
ng serve
All components that make up the todo list itself are so called pure components.
They don't have a internal state but receive inputs and have outputs. Also, the change detection is set to OnPush. That means that
they will only rerender themselves if a input changes or a event (like a click or input) is triggered.
Only the todos.component.ts has all the logic in it to wire everything up correctly. Such a component is called higher order component.
The todo.service.ts is a immutable service:
After every operation it create a new list of todos or event new todo objects (see update method). This prevents rendering issues when working
with the OnPush change detection strategy.