TypeScript. Type error when creating new object with spread operator

What you are trying to do is wrong because you do not consider encapsulation. _date is a private field that should not be accessed outside of the object. You defined the getter date, use it.

You should not use

this._date = todo._date;

but

this._date = todo.date;.

Here is an example :

class Todo {
  private _date: Date;
  public name: string;

  constructor(todo) {
    this._date = todo.date;
    this.name = todo.name;
  }

  get date(): Date {
    return this._date;
  }
}

const todo = new Todo(null);

const modifiedTodos1 = new Todo(todo);

const modifiedTodos2 = new Todo({
  ...todo,
  date: new Date(),
});

Also note that it will not work if you strongly type todo in the constructor like:

  constructor(todo: Todo) {
    this._date = todo.date;
    this.name = todo.name;
  }

Because typescript is waiting for a Todo object that you do not provide using the spread operator (no date function).

To adress this issue I recommend you to specify an interface that will only contains your setters data.

interface ITodo {
  date: Date,
  name: string,
}

class Todo {
  private _date: Date;
  public name: string;

  constructor(todo: ITodo) {
    this._date = todo.date;
    this.name = todo.name;
  }

  get date(): Date {
    return this._date;
  }
}

const todo = new Todo(null);

const modifiedTodos1 = new Todo(todo);

const modifiedTodos2 = new Todo({
  ...todo,
  date: new Date(),
});