Our app accepts the following five actions:

• FETCH_TODOS: To fetch a new list of todo items—{ type: 'FETCH_TODOS', todos: [] }
• ADD_TODO: To insert a new todo item—{ type: 'ADD_TODO', title: 'Test ToDo app' }
• TOGGLE_TODO: To toggle the completed value of a todo item—{ type: 'TOGGLE_TODO', id: 'xxx' }
• REMOVE_TODO: To remove a todo item—{ type: 'REMOVE_TODO', id: 'xxx' }
• FILTER_TODOS: To filter todo items—{ type: 'FILTER_TODOS', filter: 'completed' }