React fuctional components don't have a
this
variable, so remove all references to it. In App.js you should have:
<List todos={todos} ts={setTodos} />
and in List.js:
const deleteTask = (id) => {
const newTodoList = props.todos.filter((currTask) => {
return currTask.id !== id;
});
props.ts(newTodoList);
};