How to use pinia in vue 3

Welcome to our complete guide on how to use pinia in Vue 3! Pinia is a state management library for Vue 3 applications. It offers a simple and efficient way to manage your application’s state, allowing you to easily share data between components and maintain a consistent state throughout your application.

Pinia is built around the concept of stores, which are containers for your application’s state. Each store represents a specific part of your application’s state and provides a set of methods to interact with that state. With pinia, you can create multiple stores to organize your state in a modular way, making it easier to manage and maintain as your application grows.

In this guide, we will walk you through the process of setting up pinia in your Vue 3 project, creating stores, accessing state and methods from your components, and handling state mutations and subscriptions. We will also cover advanced topics such as modules, plugins, and testing. By the end of this guide, you will have a solid understanding of how to effectively use pinia in your Vue 3 applications.

So whether you are new to state management in Vue 3 or already have experience with other libraries such as Vuex, this guide will serve as a comprehensive resource to help you harness the power of pinia and take your Vue 3 applications to the next level.

Why Pinia is a great choice for state management in Vue 3

When working with Vue 3, choosing the right state management library can greatly impact the efficiency and maintainability of your project. Pinia is an excellent choice for several reasons.

1. Built specifically for Vue 3

Pinia is a state management library that is designed to work seamlessly with Vue 3. It takes full advantage of the Composition API and other new features introduced in Vue 3, making it a powerful tool for managing the state of your application.

2. Simple and intuitive API

The API provided by Pinia is straightforward and easy to understand. It follows the same reactive pattern as Vue 3, making it familiar to developers who are already familiar with Vue. This simplicity makes it easier to get started with Pinia and reduces the learning curve for new developers.

3. Optimized performance

Pinia is built with performance in mind. It leverages the reactivity system of Vue 3 to efficiently update and synchronize the state across components. This means that changes to the state are propagated only to the components that depend on them, resulting in improved performance and reduced overhead.

4. Official support from the Vue team

Pinia is developed and maintained by the same team behind Vue, which ensures that it is aligned with the best practices and recommendations of the Vue ecosystem. This official support guarantees timely updates, bug fixes, and compatibility with future versions of Vue.

5. Strong TypeScript integration

If you are using TypeScript in your Vue 3 project, Pinia provides excellent TypeScript support out of the box. It offers type-safe access to the state and getters, enabling you to catch errors and ensure type correctness at compile time.

6. Rich ecosystem

Pinia benefits from the Vue ecosystem and has a wide range of plugins and add-ons available. Whether you need to integrate with other libraries or extend the functionality of Pinia, you can find many community-contributed packages to help you.

Feature	Pinia	Other State Management Libraries
Built for Vue 3	✅	❌
Simple API	✅	❌
Optimized performance	✅	❌
Official support from Vue team	✅	❌
TypeScript integration	✅	❌
Rich ecosystem	✅	❌

As you can see, Pinia offers several advantages over other state management libraries, making it a great choice for Vue 3 projects. Whether you are a beginner or an experienced Vue developer, Pinia can help you build scalable and maintainable applications.

Installation and setup of Pinia in a Vue 3 project

1. Install Pinia

To get started with Pinia in your Vue 3 project, you first need to install it using NPM or Yarn. Open your terminal and run the following command:

NPM:

npm install pinia

Yarn:

yarn add pinia

2. Create a store

Next, you need to create a store for your application. A store is where you store your application state and define actions and getters to manipulate and access that state. To create a store, create a new file with a “.ts” extension (e.g. “store.ts”) and add the following code:

import { defineStore } from 'pinia';

export const useStore = defineStore('store', {
// state, actions, getters
});

3. Register Pinia plugin

In your main entry file of your Vue 3 project (e.g. “main.ts”), import and register Pinia as a plugin. Add the following code:

import { createPinia } from 'pinia';

import { createApp } from 'vue';
import App from './App.vue';
const pinia = createPinia();
const app = createApp(App);
app.use(pinia);
app.mount('#app');

4. Usage in components

Now that you have installed Pinia and registered it as a plugin, you can use it in your Vue components. Import the store from the file you created in step 2 and use it in your components:

import { useStore } from './store';

export default {
setup() {
const store = useStore();
// Access state, actions, and getters
const state = store.state;
const action = store.action;
const getter = store.getter;
// Use state, actions, and getters in your component logic
return {
state,
action,
getter,
};
},
};

Congratulations! You have successfully installed and set up Pinia in your Vue 3 project. You can now start using the Pinia store to manage your application state.

Understanding the core concepts of Pinia

Pinia is a state management library for Vue 3 that provides a reactive and type-safe approach to managing the state of your application. To effectively use Pinia, it’s important to understand some of its core concepts.

Store

A store in Pinia represents a single source of truth for the state of your application. It contains the data and provides methods to interact with that data. Each store is defined as a class, which is then instantiated to create a store instance.

State

The state is the data managed by a store. It represents the current state of your application and can be accessed or modified using the store’s methods. The state is reactive, meaning any changes to it will automatically trigger updates in the components that depend on that state.

Actions

Actions in Pinia are methods defined in a store that are responsible for modifying the state. They can be asynchronous and can handle complex logic before updating the state. Actions can be triggered by events or user interactions and are typically called from components.

Getters

Getters are methods defined in a store that compute derived state from the existing state. They provide a way to transform or combine data from the state to provide a more specialized view of the state. Getters are reactive and can be accessed from components just like the state.

Mutations

Mutations are methods defined in a store that directly modify the state. Unlike actions, mutations should not have any side effects or perform asynchronous operations. They are typically used to update the state when a simple change is needed.

Modules

Modules in Pinia are used to organize the store instances into namespaces. They provide a way to split the state management into smaller and more manageable pieces. Modules can have their own state, actions, getters, and mutations, and can be nested to create a hierarchical structure.

Plugins

Plugins in Pinia are reusable pieces of functionality that can be added to stores or the entire application. They can extend the functionality of stores by adding new methods, hooks, or components. Plugins can be used to implement features like persistence, logging, or API integration.

Devtools

Pinia has built-in devtools support that allows you to inspect and debug the state of your application. The devtools provide a visual representation of the stores, the state, and the changes made to it. It also allows you to time-travel and replay state changes for debugging purposes.

Reactivity

Pinia uses Vue 3’s reactivity system to automatically track dependencies and update components when the state changes. This means that any changes to the state will trigger re-renders in the components that depend on that state. Pinia also provides fine-grained reactivity tracking using its store API.

Type-safety

Pinia leverages TypeScript to provide type-safety in your Vuex store. This means that you can leverage TypeScript’s static type checking to catch potential bugs and provide better autocompletion and documentation for the state, actions, getters, and mutations in your store.

Creating and configuring a store in Pinia

In order to use Pinia, you need to create and configure a store. A store in Pinia is essentially a reactive data container that holds the state of your application. Here’s how you can create and configure a store in Pinia:

Step 1: Installing and setting up Pinia

1. Install Pinia by running the following command in your project directory:

npm install pinia

2. Import and use Pinia in your main application file, usually named “main.js” or “app.js”:

import { createApp } from 'vue'

import { createPinia } from 'pinia'
const app = createApp(App)
// Create and use Pinia
const pinia = createPinia()
app.use(pinia)
app.mount('#app')

Step 2: Creating a store

1. Create a new file for your store, for example “counter.js”.
2. Inside the file, import the required dependencies:

import { defineStore } from 'pinia'

3. Define your store using the defineStore function:

export const useCounterStore = defineStore('counter', {

state: () => ({
count: 0
}),
actions: {
increment() {
this.count++
},
decrement() {
this.count--
}
}
})

Step 3: Using the store

1. In your component, import the store:

import { useCounterStore } from '@/stores/counter'

2. Use the store by calling the useCounterStore function:

setup() {

const counterStore = useCounterStore()
return {
counterStore
}
}

Now, you can use the counterStore in your component:

• To access the state: counterStore.count
• To call an action: counterStore.increment()

Congratulations! You have successfully created and configured a store in Pinia.

Accessing and updating state in Pinia

One of the core concepts in Pinia is the use of state, which represents the data of your application. In this section, we will explore how to access and update state in Pinia.

Accessing state

To access state in Pinia, you need to use the `useStore` function provided by Pinia. This function takes the store identifier as an argument and returns an instance of the store.

Here’s an example of how to access state in Pinia:

“`js

import { useStore } from ‘pinia’

export default {

setup() {

const store = useStore(‘exampleStore’)

console.log(store.state.someProperty) // accessing state property

console.log(store.state.anotherProperty) // accessing another state property

return {

// …

}

}

}

“`

In the example above, we import the `useStore` function from Pinia and use it to retrieve an instance of the store called `exampleStore`. We can then access the state properties by using the `state` object on the store instance.

Updating state

Updating state in Pinia is done by using mutations. Mutations are functions defined in the store that are responsible for modifying the state.

To update state in Pinia, you need to call a mutation function on the store instance. Here’s an example:

“`js

import { useStore } from ‘pinia’

export default {

setup() {

const store = useStore(‘exampleStore’)

// calling a mutation to update the state

store.someMutation(‘new value’)

return {

// …

}

}

}

“`

In the example above, we call the `someMutation` function on the `exampleStore` instance and pass the new value as an argument. The mutation function will then update the state accordingly.

Note that mutations in Pinia are synchronous. If you need to perform asynchronous operations, it is recommended to use actions instead.

Summary

• To access state in Pinia, use the `useStore` function and access the state properties through the store instance.
• To update state in Pinia, define and call mutation functions on the store instance.
• Mutations in Pinia are synchronous, so use actions for asynchronous operations.

Now that you know how to access and update state in Pinia, you can start building your Vue 3 applications with ease.

Handling actions in Pinia stores

Actions are functions in Pinia stores that are responsible for performing asynchronous or side effect operations. They can be called from components or other actions.

To define an action in a Pinia store, you can use the `@action` decorator followed by the function name. The function can be either async or synchronous, depending on your needs.

“`javascript

import { defineStore, createStore } from ‘pinia’;

export const useMyStore = defineStore(‘myStore’, {

state: () => ({

// state properties

}),

actions: {

async fetchData() {

// perform asynchronous operations

},

syncOperation() {

// perform synchronous operations

},

},

});

“`

Once defined, actions can be called from a component or other actions using the `useStore()` hook or the `this.$store` property.

“`javascript

import { useMyStore } from ‘@/store/myStore’;

// in a Vue component

export default {

setup() {

const store = useMyStore();

const fetchData = async () => {

await store.fetchData();

// handle the result

};

return {

fetchData,

};

},

};

“`

Specifying return types

Actions can return values, which can be useful when you need to handle the result of an action in a component or another action. To specify the return type of an action, you can use TypeScript generics.

“`javascript

export const useMyStore = defineStore(‘myStore’, {

state: () => ({

// state properties

}),

actions: {

async fetchData(): Promise {

// perform asynchronous operations

return data;

},

},

});

“`

Accessing state and other actions

Inside an action, you can access the store’s state and other actions using the `this` keyword or by destructuring the store object.

“`javascript

export const useMyStore = defineStore(‘myStore’, {

state: () => ({

counter: 0,

}),

actions: {

increment() {

this.counter++;

},

logCounter() {

console.log(this.counter);

},

},

});

“`

Using actions in templates

In Vue templates, you can call actions using the `@click` directive or other event directives. You can access the store’s actions using the `$actions` property of the store object.

“`html

“`

Handling asynchronous actions

Asynchronous actions can be handled using `async` and `await`. You can perform asynchronous operations such as API calls, timeouts, or promises within an action.

“`javascript

export const useMyStore = defineStore(‘myStore’, {

state: () => ({

loading: false,

data: null,

}),

actions: {

async fetchData() {

this.loading = true;

try {

// perform asynchronous operations

const response = await fetch(‘https://api.example.com/data’);

this.data = await response.json();

} catch (error) {

console.error(error);

} finally {

this.loading = false;

}

},

},

});

“`

In the above example, the `fetchData` action sets the `loading` state to `true`, makes the API call, and updates the `data` state with the response. If any error occurs, it is logged to the console. Finally, the `loading` state is set to `false` regardless of the result.

Calling actions from other actions

You can call one action from another action within the same store. This can be useful when you need to reuse functionality or chain multiple actions together.

“`javascript

export const useMyStore = defineStore(‘myStore’, {

state: () => ({

counter: 0,

}),

actions: {

increment() {

this.counter++;

},

doubleIncrement() {

this.increment();

this.increment();

},

},

});

“`

In the above example, the `doubleIncrement` action calls the `increment` action twice, effectively doubling the counter value.

Using getters in Pinia to derive computed state

In Pinia, getters are a way to compute and derive state based on the values in your store. They allow you to create computed properties that automatically update when the underlying state changes.

Defining getters

To define a getter in Pinia, you need to use the get method provided by the defineStore function when creating your store. Here’s an example:

“`javascript

import { defineStore } from ‘pinia’

export const useStore = defineStore(‘myStore’, {

state: () => ({

count: 0,

}),

getters: {

doubleCount(state) {

return state.count * 2

},

},

})

“`

In this example, we’ve defined a getter called doubleCount that returns the double of the count state.

Using getters

Once you’ve defined a getter, you can access it in your component using the $store property and the name of the getter. Here’s an example:

“`javascript

import { defineComponent } from ‘vue’

import { useStore } from ‘./store’

export default defineComponent({

setup() {

const store = useStore()

console.log(store.doubleCount)

},

})

“`

In this example, we’re accessing the doubleCount getter by using store.doubleCount. This will automatically compute the value of the getter based on the current state of the store.

Using getters in templates

You can also use getters directly in your templates. Pinia provides a shorthand syntax to access getters, using the $ sign followed by the name of the getter. Here’s an example:

“`html

“`

In this example, we’re using the $doubleCount syntax to display the value of the doubleCount getter in the template.

Conclusion

Getters in Pinia are a powerful way to derive computed state based on the values in your store. They provide a convenient and reactive way to update and use computed properties in your Vue components.

Working with modules in Pinia for better organization

When working on complex Vue applications, it is important to organize your code in a way that is maintainable and scalable. Pinia provides the ability to work with modules to achieve this goal. Modules in Pinia allow you to divide your store into smaller, more manageable pieces.

Creating a module

To create a module in Pinia, you need to define a separate file for it. This file will export a function that returns a Pinia store with its own state, getters, mutations, and actions.

Here’s an example of creating a module for a shopping cart system:

“`javascript

// cart.js

import { defineStore } from ‘pinia’

export const useCartStore = defineStore(‘cart’, {

state: () => ({

items: [],

total: 0,

}),

getters: {

itemCount: (state) => state.items.length,

},

actions: {

addItem(item) {

this.items.push(item)

},

removeItem(item) {

const index = this.items.indexOf(item)

if (index > -1) {

this.items.splice(index, 1)

}

},

},

})

“`

By defining the store as a module, you can keep related state, getters, mutations, and actions together in one file.

Using a module

To use a module, you need to import it and create an instance of the store. You can then access the store’s state, getters, mutations, and actions using the provided API.

Here’s an example of using the `useCartStore` module in a component:

“`vue

“`

Using modules in Pinia helps to keep your code organized and promotes reusability. It also makes it easier to understand and maintain your application, especially as it grows in complexity.

Conclusion

In this article, we learned about working with modules in Pinia for better organization. Modules allow you to divide your store into smaller, more manageable pieces. This improves code maintainability and scalability, especially in complex Vue applications. By creating modules, you can keep related state, getters, mutations, and actions together, making it easier to work with your store.

Testing Pinia stores in Vue 3 applications

Testing is an important part of developing any application. With Pinia, testing your Vue 3 applications becomes easier as it provides a clear and straightforward way to test your stores.

Setting up the test environment

Before starting with the actual testing, you need to set up the test environment. First, make sure you have the necessary dependencies installed. You will need Jest as the testing framework along with the Vue Test Utils library.

To install Jest and Vue Test Utils, you can run the following command:

npm install --save-dev jest @vue/test-utils

Once the dependencies are installed, you can create a new file for your store tests. In this file, you can import the necessary modules and configure the test environment. Here’s an example:

import { mount } from '@vue/test-utils'

import { createPinia } from 'pinia'
import { useCounterStore } from '@/stores/counter'
const pinia = createPinia()
beforeEach(() => {
pinia.state.value = 0
pinia.state.step = 1
})

Writing tests for Pinia stores

Once the test environment is set up, you can start writing tests for your Pinia stores. Pinia provides a way to mount the store and access its state and actions for testing purposes.

Here’s an example of a test that checks if the counter store increments the value correctly:

test('increments the counter value', () => {

const store = useCounterStore(pinia)
store.increment()
expect(store.value).toBe(1)
})

In this test, we mount the counter store using the `useCounterStore` function provided by Pinia. Then, we call the `increment` action and assert that the value is incremented correctly.

You can also test computed properties and getters in your Pinia stores. Here’s an example:

test('computed property returns the correct value', () => {

const store = useCounterStore(pinia)
expect(store.computedProperty).toBe(10)
})

In this example, we assert that the computed property `computedProperty` returns the correct value.

Additional tips

When testing Pinia stores, it’s important to keep in mind the following tips:

• Make sure to reset the store state before each test using the `beforeEach` hook.
• Use the `mount` function from Vue Test Utils to mount the store.
• Access the store’s state and actions directly to test their functionality.
• Assert the expected values using the `expect` function.

By following these tips and guidelines, you can effectively test your Pinia stores in Vue 3 applications and ensure their functionality and reliability.

Advanced features and best practices with Pinia

1. Computed properties

Pinia provides the ability to create computed properties within your stores. Computed properties are functions that derive their values from the state of the store and are reactive, meaning they will automatically update when dependent state variables change.

To create a computed property, you can define a method inside your store with the @computed decorator. This method can then be accessed like a normal property from your components.

import { defineStore, useStore } from 'pinia';
const useCounterStore = defineStore('counter', {
state: () => ({
count: 0,
}),
getters: {
doubleCount: state => state.count * 2,
},
actions: {},
});
export function useCounter() {
return useStore('counter');
}
// In component
import { useCounter } from './counter';
export default {
setup() {
const counter = useCounter();
return {
doubleCount: counter.doubleCount,
};
},
};

2. Actions

Actions in Pinia are methods defined inside a store that perform asynchronous or synchronous operations. They can be used to modify the state of the store or perform other side effects.

To define an action, you can use the @action decorator. Actions can be called from your components using the store.actionName() syntax.

import { defineStore, useStore } from 'pinia';
const useCounterStore = defineStore('counter', {
state: () => ({
count: 0,
}),
getters: {},
actions: {
async increment() {
await someAsyncOperation();
this.count++;
},
},
});
export function useCounter() {
return useStore('counter');
}
// In component
import { useCounter } from './counter';
export default {
setup() {
const counter = useCounter();
return {
increment: counter.increment,
};
},
};

3. Modules

Pinia allows you to modularize your stores using store modules. Store modules can contain their own state, getters, actions, and can be used to organize and encapsulate related logic.

To create a store module, you can use the defineStore function with a unique name for the module. Store modules can be accessed and used in the same way as normal stores.

import { defineStore, useStore } from 'pinia';
const useUserStore = defineStore('user', {
state: () => ({
name: '',
}),
getters: {},
actions: {},
});
const usePostStore = defineStore('post', {
state: () => ({
posts: [],
}),
getters: {},
actions: {},
});
// In component
import { useUserStore, usePostStore } from './stores';
export default {
setup() {
const userStore = useUserStore();
const postStore = usePostStore();
return {
name: userStore.name,
posts: postStore.posts,
};
},
};

4. Reactivity and composition

Pinia leverages Vue 3’s reactivity system for efficient updates and re-rendering of components. This allows you to easily compose and combine stores and react to changes in store state.

When a store’s state changes, any component that is using the store will automatically re-render and update its view. You can also use the watch API to react to specific changes in store state.

import { watch } from 'vue';
import { useCounterStore } from './counter';
export default {
setup() {
const counterStore = useCounterStore();
watch(() => counterStore.count, (newValue, oldValue) => {
console.log('Count changed!', newValue, oldValue);
});
return {};
},
};

By following these advanced features and best practices with Pinia, you can build more robust and scalable Vue applications with better state management. Pinia’s simplicity and integration with Vue make it a powerful tool for managing state in your Vue 3 projects.

FAQ:

What is Pinia?

Pinia is a state management system for Vue.js 3.

Why should I use Pinia?

You should use Pinia because it provides a simple and efficient way to manage the state of your Vue.js 3 applications.

How do I install Pinia?

To install Pinia, you can use the following command: npm install pinia.

Can I use Pinia with Vue 2?

No, Pinia is specifically designed for Vue.js 3 and does not work with Vue 2.

How do I create a store using Pinia?

To create a store using Pinia, you need to define a class that extends the Pinia Store and use the provided decorator to define the state and actions of the store.

What is the difference between Pinia and Vuex?

The main difference between Pinia and Vuex is that Pinia is specifically designed for Vue.js 3, while Vuex is designed for Vue.js 2. Pinia also provides a more simple and efficient way to manage state compared to Vuex.

Can I use Pinia with TypeScript?

Yes, Pinia fully supports TypeScript.