Method Chaining

[bliu13]

Hi, I have been working on mocking packages with method chaining, but I was having undefined exceptions for something like this:

import { LibraryClass } from 'library';

const client = LibraryClass(config);
client.message.send('hi vitest').done();

This is what I did to mock the library:

vi.mock('library', () => ({
  LibraryClass: vi.fn().mockImplementation(() => ({
    message: {
      send: vi.fn().mockImplementation(() => ({
        done: vi.fn(),
      })),
    },
  })),
}));

and I have tried this variant as well:

vi.mock('library', () => ({
  LibraryClass: vi.fn().mockReturnValue({
    message: {
      send: vi.fn().mockReturnValue({
        done: vi.fn(),
      }),
    },
  }),
}));

When I debugged the code on Visual Studio Code, the debugger was showing that client.message.send('hi vitest') returns an object with this property:

{
  done: vi.fn()
}

The debugger should show that client.message.send('hi vitest')['done'] and client.message.send('hi vitest').done was defined, but client.message.send('hi vitest').done() was undefined. I am not sure how to get the method chaining to work.

[bliu13]

I got the undefined behavior to work when using Visual Studio Code's debugger by changing from done: vi.fn() to done: () => vi.fn(), where both of these work in the debug mode, but when I run the test in the command line, vitest is still saying it's undefined.

vi.mock('library', () => ({
  LibraryClass: vi.fn().mockImplementation(() => ({
    message: {
      send: vi.fn().mockImplementation(() => ({
        done: () => vi.fn(),
      })),
    },
  })),
}));

vi.mock('library', () => ({
  LibraryClass: vi.fn().mockReturnValue({
    message: {
      send: vi.fn().mockReturnValue({
        done: () => vi.fn(),
      }),
    },
  }),
}));

For some reason I was under some assumption that vi.fn() would create a method that is executable, but it doesn't appear to be the case? Maybe someone can provide an explanation? Maybe there is something I did not understand about Javascript or Vitest?