TypeScript: Todo item with constructor

todo-item.ts

class TodoItem {
  id: string;
  isDone: boolean;
  title: string;

  constructor(properties) {
    this.id = properties.id;
    this.isDone = properties.isDone;
    this.title = properties.title;
  }

  save(): Promise<void> {
    return fetch("/todo/" + this.id, {
      body: JSON.stringify(this),
      method: "POST",
    })
      .then(() => undefined);
  }
}