为什么数组中的原始项会被Object.assign?

我有一个单元测试,它产生了一些我没想到的东西:

背景:我正在用角度/测试驱动开发制作一个简单的todo列表。

问题:当我对数组中的项调用editTask时,它会更改该项的值。但是,我看不到它在原始数组中是如何变化的,因为在我测试的方法中从未访问过原始数组。请帮助我连接如何更改原始阵列?看来对象.assign为什么要这么做?

 describe('editTask', () => {
    it('should update the task by id', () => {
      const dummyTask1 = { id: 1, name: 'test', status: false };
      service.tasks.push(dummyTask1); //refers to TestBed.get(TaskService)
      const id = 1;
      const values = { name: 'cat', status: false };

      service.editTask(id, values);
      console.log(service.tasks); // why does this log this object? [Object{id: 1, name: 'cat', status: false}]
      expect(service.tasks[0].name).toEqual(values.name); // Test passes
    });
  });

  editTask(id, values) {
    const task = this.getTask(id);

    if (!task) {
      return;
    }

    Object.assign(task, values); //How does this line change the array?

    return task;
  }

  getTask(id: number) {
    return this.tasks.filter(task => task.id === id).pop(); //is this altering the original array somehow?
  }

export class TaskService {
  tasks: any = [];
  lastId = 0;

  constructor() { }

  addTask(task) {
    if (!task.id) {
      task.id = this.lastId + 1;
    }

    this.tasks.push(task);
  }

  editTask(id, values) {
    const task = this.getTask(id);

    if (!task) {
      return;
    }

    Object.assign(task, values);

    return task;
  }

  deleteTask(id: number) {
    this.tasks = this.tasks.filter(task => task.id !== id);
  }

  toggleStatus(task) {
    const updatedTask = this.editTask(task.id, { status: !task.status});

    return updatedTask;
  }

  getTasks() {
    return of(this.tasks);
  }

  getTask(id: number) {
    return this.tasks.filter(task => task.id === id).pop();
  }
}

以下是github回购协议: https://github.com/capozzic1/todo-tdd