Other improvements

Let's implement some other improvements to our todo list application:

Add a checkbox to mark a todo item as completed
Add a filter to show only the completed items, only the uncompleted items, or all items
Add a button to remove all completed items
Disable the Remove All button when there are no items to remove
Disable the Remove Completed button when there are no completed items

Completing and filtering a todo item

The TodoItem class already has a boolean flag called completed that indicates if the todo item is completed or not.

We will:

Create the Filter enum:

export enum Filter {
  showAll = 'Showing ALL',
  showCompleted = 'Showing COMPLETED',
  showActive = 'Showing ACTIVE',
}

Add the filter state to the State class:

export class State {
  todoList: TodoList;
  readonly filter: Filter;

constructor({todoList, filter}: { todoList: TodoList, filter: Filter }) {
    this.todoList = todoList;
    this.filter = filter;
  }  

  withTodoList(todoList: TodoList): State {
    return new State({ todoList: todoList, filter: this.filter });
  }
  
  withFilter(filter: Filter): State {    
    return new State({todoList: this.todoList, filter: filter});
  }

  static initialState: State = new State({ 
    todoList: TodoList.empty, 
    filter: Filter.showAll 
  });
}

Add a checkbox to the TodoItemComponent that allows the user to mark the todo item as completed. The checkbox dispatches the ToggleTodoAction action.
Modify the TodoItemComponent so that it only shows the item if it matches the filter.
Add the RemoveCompletedButton component that dispatches the RemoveCompletedTodosAction. The button is disabled when there are no completed items.
Modify the RemoveAllButton component so that it is disabled when there are no items to remove.
Add the FilterButton component that dispatches the NextFilterAction action. This button text is based on the current filter: "Showing all", "Showing completed", or "Showing active".

Try it yourself

Click the "Add Random Todo" a few times, to add some items to the list. Then, mark some of them as completed, and click the "Showing all" button to see how the filter works.

Read the code below and try to understand how it works.

Completing and filtering a todo item​

Try it yourself​

Completing and filtering a todo item

Try it yourself