How to properly pass the this value when unit testing a Vuex action in TypeScript?

Question

How to properly pass the this value when unit testing a Vuex action in TypeScript?

Currently, I am working with Vuex in a TypeScript configuration and facing challenges while attempting to unit test an action due to difficulty in setting the this parameter of the action method.

The action looks something like this:

export const login: ActionHandler<AuthState, RootState> = ({ commit },
  creds: { email: string, password: string }) => {
};

Here is how the test is structured:

  describe('actions', () => {
    test('login should call API with credentials', () => {
      (ApiService.post as jest.Mock).mockResolvedValue({
        data: { userId: 1234 }
      });
      const commit = jest.fn();
      login({ commit }, { email: '<a href="/cdn-cgi/l/email-protection" class="__cf_email__" data-cfemail="13666076617d727e7653747e727a7a3a767077">[email protected]</a>', password: 'Pa$$w0rd123' });
    });
  });

The issue arises from the fact that the ActionHandler has a signature like:

login(this: Store<RootState>, injectee: ActionContext<AuthState, RootState>, payload?: any): any

.

As a result, TypeScript presents the following error message:

The 'this' context of type 'void' is not assignable to method's 'this' of type 'Store<RootState>'.ts(2684)

I am struggling to determine how to assign an instance of Store<RootState> as the this of the login action. Could it be possible that I am approaching this incorrectly? While I understand that this problem might not occur if I were using vanilla JS, my preference is to continue utilizing TypeScript if feasible.

typescript unit-testing vue.js jestjs vuex

Answer 1

Answer №1

I have discovered two approaches to tackle a similar issue. Feel free to give them a try.

1. Approach: Binding `this` (highly recommended)

To make it work, you need to bind your store to this and utilize the bound action:

// Bind
const loginBound = login.bind(store)

// Call
loginBound( /* ... */ );

In order for this solution to be effective, you may need to define additional mocks. Refer to "Appendix: Complete code solution" below for details.

2. Approach: Utilize `Function` casting

By opting for this method, you can satisfy Typescript requirements, but essentially you are just sidestepping the actual problem (essentially turning off type checks for the action).

// Bind
const loginCast = login as Function

// Call
loginCast( /* ... */ );

Appendix: Complete code solution

If utilizing the 1st approach (binding this), you will likely need to provide a comprehensive action context. Here is how the entire solution should look like:

describe('actions', () => {
  test('login should call api with credentials', () => {
    (ApiService.post as jest.Mock).mockResolvedValue({
      data: { userId: 1234 }
    });

    // Bind `this`
    const loginBound = login.bind(store)

    // Providing full action context
    const actionContext: ActionContext<AuthState, RootState> = {
      dispatch: jest.fn(),
      commit: jest.fn(),
      state: {}, // Your auth state mock goes here
      getters: {},
      rootState: {}, // Your root state mock goes here
      rootGetters: {}
    };

    // Call
    loginBound(actionContext, { email: '<a href="/cdn-cgi/l/email-protection" class="__cf_email__" data-cfemail="691c1a0c1b0708040c290e04080005470a06">[email protected]</a>', password: 'Pa$$w0rd123' });
  });
});

Answer 2

I have discovered two approaches to tackle a similar issue. Feel free to give them a try.

1. Approach: Binding `this` (highly recommended)

To make it work, you need to bind your store to this and utilize the bound action:

// Bind
const loginBound = login.bind(store)

// Call
loginBound( /* ... */ );

In order for this solution to be effective, you may need to define additional mocks. Refer to "Appendix: Complete code solution" below for details.

2. Approach: Utilize `Function` casting

By opting for this method, you can satisfy Typescript requirements, but essentially you are just sidestepping the actual problem (essentially turning off type checks for the action).

// Bind
const loginCast = login as Function

// Call
loginCast( /* ... */ );

Appendix: Complete code solution

If utilizing the 1st approach (binding this), you will likely need to provide a comprehensive action context. Here is how the entire solution should look like:

describe('actions', () => {
  test('login should call api with credentials', () => {
    (ApiService.post as jest.Mock).mockResolvedValue({
      data: { userId: 1234 }
    });

    // Bind `this`
    const loginBound = login.bind(store)

    // Providing full action context
    const actionContext: ActionContext<AuthState, RootState> = {
      dispatch: jest.fn(),
      commit: jest.fn(),
      state: {}, // Your auth state mock goes here
      getters: {},
      rootState: {}, // Your root state mock goes here
      rootGetters: {}
    };

    // Call
    loginBound(actionContext, { email: '<a href="/cdn-cgi/l/email-protection" class="__cf_email__" data-cfemail="691c1a0c1b0708040c290e04080005470a06">[email protected]</a>', password: 'Pa$$w0rd123' });
  });
});

Answer 3

Answer №2

This is the approach I took

(authenticate as Function)({ commit: jest.fn() }, { email: 'username.....', password: '..' });

In my specific case, I have a detailed state structure:

import { Module } from 'vuex';

const data: Module<any, any> = {
  state: { .... },
  mutations: { .... },
  getters: { ... },
  actions: {
    setData({ commit }, newData: string[]) {
      commit('SET_DATA_LIST', newData);
    }
  }
}

When testing with jest, I execute it like this:

(data.actions!.setData as Function)(context, ['1001', '1002']);

This particular line eliminates TypeScript validations for ActionContext<any, any>

Answer 4

This is the approach I took

(authenticate as Function)({ commit: jest.fn() }, { email: 'username.....', password: '..' });

In my specific case, I have a detailed state structure:

import { Module } from 'vuex';

const data: Module<any, any> = {
  state: { .... },
  mutations: { .... },
  getters: { ... },
  actions: {
    setData({ commit }, newData: string[]) {
      commit('SET_DATA_LIST', newData);
    }
  }
}

When testing with jest, I execute it like this:

(data.actions!.setData as Function)(context, ['1001', '1002']);

This particular line eliminates TypeScript validations for ActionContext<any, any>

How to properly pass the this value when unit testing a Vuex action in TypeScript?

Answer №1

1. Approach: Binding `this` (highly recommended)

2. Approach: Utilize `Function` casting

Appendix: Complete code solution

Answer №2

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How to properly pass the this value when unit testing a Vuex action in TypeScript?

Answer №1

1. Approach: Binding this (highly recommended)

2. Approach: Utilize Function casting

Appendix: Complete code solution

Answer №2

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1. Approach: Binding `this` (highly recommended)

2. Approach: Utilize `Function` casting