Introducing Vuex in your projects
How to add and use Vuex in existing projects, with an eye for testing.
- Denny Biasiolli -

WHO AM I
Denny Biasiolli
Freelance Full Stack Developer
Front End Developer UX/ UI
Fingerprint Supervision Ltd
Savigliano (CN) - Italy
Volunteer in a retirement home,
performing recreational activities
@dennybiasiolli
denny.biasiolli@gmail.com
dennybiasiolli.com

EXAMPLE APP

EXAMPLE APP
Structure

EXAMPLE APP
Main component, data()
export default {
name: 'Home',
data() { // component's state
return {
availableNumbers: [...Array(90).keys()]
.map((i) => i + 1),
extractedNumbers: [],
};
},
// ...
};

EXAMPLE APP
Main component, computed
export default {
// ...
computed: { // component's getters
ascendingExtractedNumbers() {
return [...this.extractedNumbers].sort((a, b) => a - b);
},
},
// ...
};

EXAMPLE APP
Main component, methods
export default {
// ...
methods: { // component's actions/mutations
handleExtract() {
const index = Math.floor(
Math.random() * this.availableNumbers.length);
const extracted = this.availableNumbers
.splice(index, 1);
this.extractedNumbers = this.extractedNumbers
.concat(extracted);
},
},
};

EXAMPLE APP
Main component template
<button @click="handleExtract">Extract</button>
<h1>
Extracted:
{{ extractedNumbers[extractedNumbers.length - 1] }}
</h1>
<DisplayNumbers title="Available numbers"
:numbers="availableNumbers" />
<DisplayNumbers title="Extracted numbers"
:numbers="ascendingExtractedNumbers" />

EXAMPLE APP
DisplayNumbers component
<v-card elevation="2">
<v-card-title>{{ title }}</v-card-title>
<v-card-text>
<v-chip v-for="n of numbers" :key="n" class="ma-1">
{{ n }}
</v-chip>
</v-card-text>
</v-card>
export default {
name: 'DisplayNumbers',
props: {
title: String,
numbers: Array,
},
};

COMPONENT TESTS
DisplayNumbers
import { shallowMount } from '@vue/test-utils';
import DisplayNumbers from '@/components/DisplayNumbers.vue';
test('renders as expected', () => {
const wrapper = shallowMount(DisplayNumbers, {
stubs: ['v-container', 'v-card', 'v-card-title', 'v-card-t
propsData: {
title: 'title text',
numbers: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10],
},
});
expect(wrapper).toMatchSnapshot();
});

COMPONENT TESTS
Home #1
import { shallowMount } from '@vue/test-utils';
import Home from '@/views/Home.vue';
const shallowMountComponent = () => shallowMount(Home, {
stubs: ['v-container', 'v-btn', 'v-row', 'v-col'],
});
test('renders as expected', () => {
const wrapper = shallowMountComponent();
expect(wrapper).toMatchSnapshot();
});
// ...

COMPONENT TESTS
Home #2
// ...
test('extracts a number and render as expected', async () => {
jest.spyOn(global.Math, 'random')
.mockReturnValueOnce(0.123456789)
.mockReturnValueOnce(0.987654321);
const wrapper = shallowMountComponent();
wrapper.vm.handleExtract();
await wrapper.vm.$nextTick();
expect(wrapper).toMatchSnapshot();
wrapper.vm.handleExtract();
await wrapper.vm.$nextTick();
expect(wrapper).toMatchSnapshot();
jest.spyOn(global.Math, 'random').mockRestore();
});

ONE-WAY DATA FLOW

STATE FLOW SUMMARY
Flow process Vue.js component
State data and computed
View <template>
Actions methods

STATE PROBLEM

Solution 1: Moving state to parent components
move data() from Home to App
receiving numbers in Home and Footer as props
emitting an event when "Extract" button is clicked
in Home
handling extract event in App component, moving
methods from Home to App
updating tests

PROS
fast and easy in small apps
keep the state in the components where it is used
(if there is no need to pass it to other components)
no extra dependencies
testing sub-components with propsData and
snapshots

CONS
multiple views may depend on the same piece of
state
actions from different views may need to mutate the
same piece of state
messy on big apps, lots of extra code for passing
props, emitting events
hard to follow state changes on many levels
what is causing a data change?

WHAT IS VUEX?
A state management pattern/library
for Vue.js applications.
It serves as a centralized store for all
the components in an application,
with rules ensuring that the state can
only be mutated in a predictable
fashion.
https://vuex.vuejs.org/

WHEN SHOULD I USE IT?
There's a good quote from Dan Abramov,
the author of Redux:
Flux libraries are like glasses: you’ll
know when you need them.
https://vuex.vuejs.org/

WHEN SHOULD I USE IT?
It's a trade-off between short term and long term productivity.
If you jump right into Vuex, it may feel verbose and daunting.
But if you are building a medium-to-large-scale SPA, chances are you have run into
situations that make you think about how to better handle state outside of your Vue
components, and Vuex will be the natural next step for you.
https://vuex.vuejs.org/

VUEX FLOW

INSTALL VUEX
or
<script src="/path/to/vue.js"></script>
<script src="/path/to/vuex.js"></script>
npm install --save vuex
# or
yarn add vuex # https://yarnpkg.com/
# or
npx @vue/cli add vuex # https://cli.vuejs.org/
import Vue from 'vue';
import Vuex from 'vuex';
Vue.use(Vuex);
https://vuex.vuejs.org/installation.html

CONFIGURE VUEX
Creating the store
// src/store/index.js
import Vue from 'vue';
import Vuex from 'vuex';
Vue.use(Vuex);
export default new Vuex.Store({
state: { /* ... */ },
mutations: { /* ... */ },
});
https://vuex.vuejs.org/guide/

CONFIGURE VUEX
Enabling this.$store inside Vue components
// src/main.js
// ...
import store from './store';
new Vue({
store, // same as `store: store`
// ...
});
https://vuex.vuejs.org/guide/

CONCEPTS: STATE
Creation
new Vuex.Store({
state: {
count: 0
},
// ...
});
https://vuex.vuejs.org/guide/state.html

CONCEPTS: STATE
Basic usage
<div>
{{ $store.state.count }}
{{ count }}
</div>
computed: {
count () {
return this.$store.state.count;
}
}
https://vuex.vuejs.org/guide/state.html

CONCEPTS: STATE
mapState usage
import { mapState } from 'vuex';
export default {
// ...
computed: mapState({
count: state => state.count,
countAlias: 'count',
// to access local state with `this`
countPlusLocalState (state) {
return state.count + this.localCount;
}
})
};
https://vuex.vuejs.org/guide/state.html

CONCEPTS: STATE
mapState usage simplified
is the same as
mapState({
count: state => state.count
})
mapState([
'count'
])
https://vuex.vuejs.org/guide/state.html

CONCEPTS: STATE
mapState usage with other computed values
computed: {
...mapState({
// ...
}),
localComputed () { /* ... */ }
}
https://vuex.vuejs.org/guide/state.html

CONCEPTS: GETTERS
Getters are like "computed" values for a Vuex store
Creation
const store = new Vuex.Store({
state: {
count: 0
},
getters: {
countIsEven: state => {
return state.count % 2 === 0;
}
}
});
https://vuex.vuejs.org/guide/getters.html

CONCEPTS: GETTERS
Basic usage
<div>
{{ $store.getters.countIsEven }}
{{ countIsEven }}
</div>
computed: {
countIsEven () {
return this.$store.getters.countIsEven;
}
}
https://vuex.vuejs.org/guide/getters.html

CONCEPTS: GETTERS
mapGetters usage
import { mapGetters } from 'vuex';
export default {
// ...
computed: mapGetters({
countIsEvenAlias: 'countIsEven'
})
};
https://vuex.vuejs.org/guide/getters.html

CONCEPTS: GETTERS
mapGetters advanced usage
computed: {
...mapState(['count']),
...mapGetters(['countIsEven']),
localComputed () { /* ... */ }
}
https://vuex.vuejs.org/guide/getters.html

CONCEPTS: MUTATIONS
Committing a mutation is the only way to actually
change state in a Vuex store.
Creation
const store = new Vuex.Store({
state: {
count: 0
},
mutations: {
increment (state, payload=1) {
state.count += payload;
}
}
});
https://vuex.vuejs.org/guide/mutations.html

CONCEPTS: MUTATIONS
Basic usage
methods: {
increment (value) {
return this.$store.commit('increment', value);
}
}
https://vuex.vuejs.org/guide/mutations.html

CONCEPTS: MUTATIONS
mapMutations usage
import { mapMutations } from 'vuex';
export default {
// ...
methods: {
...mapMutations([
'increment'
]),
...mapMutations({
add: 'increment'
})
}
};
https://vuex.vuejs.org/guide/mutations.html

MUTATIONS MUST BE SYNCHRONOUS
Why? Because we need to have a "before" and "a er"
snapshots of the state.
If we introduce a callback inside a mutation, it makes
that impossible.
The callback is not called yet when the mutation is
committed, and there's no way to know when the
callback will actually be called. Any state mutation
performed in the callback is essentially un-trackable!
https://vuex.vuejs.org/guide/mutations.html

CONCEPTS: ACTIONS
Actions are similar to mutations, with a few
differences:
Instead of mutating the state, actions commit
mutations.
Actions can contain arbitrary asynchronous
operations.
https://vuex.vuejs.org/guide/actions.html

CONCEPTS: ACTIONS
Creation
const store = new Vuex.Store({
state: { count: 0 },
mutations: {
increment (state, payload=1) {
state.count += payload;
}
},
actions: {
incrementAsync (context, payload) {
setTimeout(() => {
context.commit('increment', payload);
}, 1000);
}
}
});
https://vuex.vuejs.org/guide/actions.html

CONCEPTS: ACTIONS
API call example
const store = new Vuex.Store({
actions: {
async getRecords (context) {
context.commit('getRecordsRequest');
try {
const results = await axios.get('/api/records/');
context.commit('getRecordsSuccess', results.data);
} catch (error) {
context.commit('getRecordsFailure', error);
}
}
}
});
https://vuex.vuejs.org/guide/actions.html

CONCEPTS: ACTIONS
Context object
context.commit to commit a mutation
context.state access the state
context.getters access the getters
context.dispatch to call other actions
https://vuex.vuejs.org/guide/actions.html

CONCEPTS: ACTIONS
mapActions usage
import { mapActions } from 'vuex';
export default {
// ...
methods: {
incrementAsyncLocal (value) {
return this.$store.dispatch('incrementAsync', value)
.then( /* ... */);
}
...mapActions(['incrementAsync']),
...mapActions({
addAsync: 'incrementAsync'
})
}
};
https://vuex.vuejs.org/guide/actions.html

EXAMPLE APP
Creating the store, default state
// src/store/index.js
import Vue from 'vue';
import Vuex from 'vuex';
Vue.use(Vuex);
export const defaultState = {
availableNumbers: [...Array(90).keys()]
.map((i) => i + 1),
extractedNumbers: [],
};

EXAMPLE APP
Creating the store, getters
// src/store/index.js
export const getters = {
ascendingExtractedNumbers(state) {
return [...state.extractedNumbers].sort((a, b) => a - b);
},
};

EXAMPLE APP
Creating the store, mutations
// src/store/index.js
export const mutations = {
extractNumber(state) {
const index = Math.floor(
Math.random() * state.availableNumbers.length);
const extracted = state.availableNumbers
.splice(index, 1);
state.extractedNumbers = state.extractedNumbers
.concat(extracted);
},
};

EXAMPLE APP
Creating the store, composing
// src/store/index.js
export default new Vuex.Store({
state: defaultState,
getters,
mutations,
});

EXAMPLE APP
Home component, data and computed function
@@ src/views/Home.vue
- data() {
- return {
- availableNumbers: [...Array(90).keys()].map((i) => i +
- extractedNumbers: [],
- };
- },
computed: {
- ascendingExtractedNumbers() {
- return [...this.extractedNumbers].sort((a, b) => a - b)
- },
+ ...mapState(['availableNumbers', 'extractedNumbers']),
+ ...mapGetters(['ascendingExtractedNumbers']),
},

EXAMPLE APP
Home component, method
@@ src/views/Home.vue
- <button @click="handleExtract">Extract</button>
+ <button @click="extractNumber">Extract</button>
methods: {
- handleExtract() {
- const index = Math.floor(Math.random() * this.available
- const extracted = this.availableNumbers.splice(index, 1
- this.extractedNumbers = this.extractedNumbers.concat(ex
- },
+ ...mapMutations(['extractNumber']),
},

MOVING TO VUEX STORE FLOW
Vue.js component Vuex store Map in
data state computed
computed getters computed
sync methods mutations methods
async methods actions methods

STORE TESTS
Default state
import { defaultState } from '@/store';
test('should have the default state', () => {
expect(defaultState).toEqual({
availableNumbers: [...Array(90).keys()].map((i) => i + 1),
extractedNumbers: [],
});
});

STORE TESTS
Getters
import { getters } from '@/store';
const { ascendingExtractedNumbers } = getters;
test('ascendingExtractedNumbers', () => {
expect(
ascendingExtractedNumbers({
extractedNumbers: [12, 56, 34]
})
).toEqual([12, 34, 56]);
});

STORE TESTS
Mutations
import { mutations } from '@/store';
const { defaultState, extractNumber } = mutations;
test('ascendingExtractedNumbers', () => {
jest.spyOn(global.Math, 'random')
.mockReturnValueOnce(0.123456789)
.mockReturnValueOnce(0.987654321);
const state = { ...defaultState };
expect(state.availableNumbers).toHaveLength(90);
// ...

STORE TESTS
Mutations
// ...
extractNumber(state);
expect(state.availableNumbers).toHaveLength(89);
expect(state.extractedNumbers).toEqual([12]);
extractNumber(state);
expect(state.availableNumbers).toHaveLength(88);
expect(state.extractedNumbers).toEqual([12, 89]);
jest.spyOn(global.Math, 'random').mockRestore();
});

STORE TESTS
Actions
Keep in mind this sample action
// export const actions = {
async getRecords (context) {
context.commit('getRecordsRequest');
try {
const results = await axios.get('/api/records/');
context.commit('getRecordsSuccess', results.data);
} catch (error) {
context.commit('getRecordsFailure', error);
}
}
// };

STORE TESTS
Actions
Mocking calls using jest
.mockReturnValue(value) for mocking sync results
.mockResolvedValue(value) for mocking async results with success
.mockRejectedValue(value) for mocking async results with failure
import axios from 'axios';
import { actions } from '@/store';
jest.mock('axios', () => ({
get: jest.fn(),
}));
https://jestjs.io/docs/mock-functions

STORE TESTS
Actions
Mocking axios success
const { getRecords } = actions;
test('getRecords success', async () => {
const commit = jest.fn();
axios.get.mockResolvedValue({ data: 'ok' });
await getRecords({ commit });
expect(commit).toHaveBeenCalledWith('getRecordsRequest');
expect(axios.get).toHaveBeenCalledWith('/api/records/');
expect(commit).toHaveBeenCalledWith(
'getRecordsSuccess', 'ok');
});

STORE TESTS
Actions
Mocking axios failures
const { getRecords } = actions;
test('getRecords failure', async () => {
const commit = jest.fn();
axios.get.mockRejectedValue('my error');
try {
await getRecords({ commit });
// Fail test if above expression doesn't throw anything
expect(true).toBe(false);
} catch (error) {
expect(commit).toHaveBeenCalledWith('getRecordsRequest');
expect(axios.get).toHaveBeenCalledWith('/api/records/');
expect(commit).toHaveBeenCalledWith(
'getRecordsFailure', 'my error');
}
});

COMPONENT TESTS USING ORIGINAL STORE
(NOT SUGGESTED)
import { shallowMount } from '@vue/test-utils';
import Home from '@/views/Home.vue';
import store from '@/store';
test('snapshot test with default props', () => {
const wrapper = shallowMount(Home, { store });
expect(wrapper).toMatchSnapshot();
});
https://vue-test-utils.vuejs.org/guides/using-with-vuex.html

COMPONENT TESTS USING ORIGINAL STORE
(NOT SUGGESTED)
Pros
fast and easy, store implementation ready-to-use
Cons
less control over store mocking and external calls
https://vue-test-utils.vuejs.org/guides/using-with-vuex.html

COMPONENT TESTS MOCKING THE STORE
import { shallowMount, createLocalVue } from '@vue/test-utils'
import Vuex from 'vuex';
import Home from '@/views/Home.vue';
const localVue = createLocalVue();
localVue.use(Vuex);
// ...
https://vue-test-utils.vuejs.org/guides/using-with-vuex.html

COMPONENT TESTS MOCKING THE STORE
// ...
describe('Home.vue', () => {
let state, getters, mutations, actions, store;
beforeEach(() => {
state = { count: 0 };
getters = { getter1: () => 'mocked return value' };
mutations = { mutation1: jest.fn() };
actions = { action1: jest.fn() };
store = new Vuex.Store({
state, getters, mutations, actions });
});
// ...
https://vue-test-utils.vuejs.org/guides/using-with-vuex.html

COMPONENT TESTS MOCKING THE STORE
// ...
test('snapshot test with default props', () => {
const wrapper = shallowMount(Home, { store, localVue });
expect(wrapper).toMatchSnapshot();
// ...
});
});
https://vue-test-utils.vuejs.org/guides/using-with-vuex.html

RECAP
What we learned today?
Why use Vuex
Install and configure a Vuex store
Test store and components

LINKS
@dennybiasiolli
vuex.vuejs.org
vue-test-utils.vuejs.org
github.com/dennybiasiolli/bingo-extraction
dennybiasiolli.com