already done
Types in header
TodoApp methods

filteredTodos in List

demo
Add Types to TodoApp
change 'filter' value
Types in List
pass complete to List - show types, change complete to boolean/, filter
add complete, pass to item (prop drilling)
TodoListItemProps, extend, id, complete (possible abstraction)
Demo how you can't add random things to TodoListItem or this.props now
add complete to List item

exercise

Add types to footer
Add onClick to button
Add types to header
Add setFilter to filter buttons
add 'addTodo' to onAdd function