Task model

Design task and status types.

Todo model

We define two core types for the Todo CLI. Status is a literal union representing a task's state: "active" or "completed". Todo represents a task with id, title, and status fields.

type Status = "active" | "completed";
interface Todo { id: string; title: string; status: Status; }

Empty task list

An empty task list is an empty array of type Todo[]. This is the CLI's initial state; the array grows as you add tasks.

const todos: Todo[] = [];
console.log(todos.length);  // 0

Exercise Write the Todo model

Define a Status type as "active" | "completed". Define a Todo interface: id: string, title: string, status: Status. Create an empty todos array and print its length.

Show example solution

type Status = "active" | "completed";

interface Todo {
  id: string;
  title: string;
  status: Status;
}

const todos: Todo[] = [];
console.log(todos.length);

Test yourself

What type should a Todo's status field be?
- boolean
- "active" | "completed"
- string
- number
Show answer

"active" | "completed" — Status is a union of literal types: "active" or "completed". This guarantees only two valid states; string would allow any value.

Complete the Status union

type Status = "active" ____ "completed";

Show answer

type Status = "active" | "completed";

Todo model parts

Status

Status type (active or completed)
Todo

Task model (id, title, status)
"active" | "completed"

Two status literals
Todo[]

Task list

Next lesson: Add and list

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