Babel const可防止突变？

Question

I'm writing tests in ES6 syntax powered by Babel, and I'm using Jest to run the tests. Here my test code:

test('case: response body contains a user, should update sessionData', () => {
  // current user info in the session
  const currentUserInfo = {
    firstName: 'User1',
    lastName: 'Old Info'
  }

  const mockSessionData = createSessionHelper(
    {
      data: {
        user: currentUserInfo
      }
    },
    mockLogger
  )

  // new user info in the body
  const newUserInfo = {
    firstName: 'User2',
    lastName: 'New Info'
  }

  const body = {
    user: newUserInfo
  }

  const result = handleSuccess({
    req: {
      sessionData: mockSessionData
    },
    body
  })

  expect(result.status).toBe(DEFAULT_SUCCESS_STATUS)
  expect(result.body).toEqual(body)
  expect(mockSessionData.get('user')).toEqual(newUserInfo)
})

As you can see, I'm using the same objects both to use as parameters to the functions I'm testing and, to match the result with my expectation.

I'm assuming here that these functions should not mutate those parameters. Is this assumption true, though?

By using Babel const , will my data remain the same, or should I still use Object.freeze() ?

Answer 1

As the reference says,

The value of a constant cannot change through re-assignment, and it can't be redeclared.

mockSessionData cannot be re-assigned. const can't and shouldn't prevent an object that mockSessionData holds a reference to from being modified. Object.freeze may be used if the object shouldn't be changed.