State and reactivity in Vue

In one of myprevious articles, I mentioned how it is possible to design a simple state manager in Vue by using observable . The Observable API has been available in Vue since version 2 however, with version 3 the reactive object is no longer directly modified but proxied into. Let's have a look how both work in detail:

In Vue 2, a reactive store might look like this:

// store.js
export const store = Vue.observable({ orders: 0 });

We can provide the components with a basic dispatch function that will collect an action with a payload and that will take care of updating the state. Also, we might want to provide a getters helper so that the store values can be reached as computed properties:

// store.js
export function dispatch(type, payload) {
    switch(type) {
        case 'increment-orders':
            Object.assign(store, { orders: store.orders + payload });
            break;
        default:
            //
    }
}

export function getters(orders) {
    return {
        orders: () => store.orders
    }
}

In our Vue component, we register the getters and use dispatch to notify the store about a user event:

<template>
    I have {{ orders }} orders on my account. 
    <a @click="increment()">add order</a>
</template>

<script>
import { dispatch } from 'store';

return {
    computed: { ...getters() },
    methods: { 
        increment() {
            dispatch('increment-orders', 1); 
        } 
    }
};
</script>

Vue 3 and the Composition API

With the introduction of the Composition API , operating with reactive properties is much simpler. The above example could be easily refactored to follow the new constructs. Here, reactive replaced the functionaltiy that observable was providing:

// store.js
import { reactive } from 'vue';

export const store = reactive({ orders: 0 });

// Component.vue
import { store, dispatch } from './store';

export default {
    setup() {
        return { store };
    },
    methods:{
        increment() {
            dispatch('increment-orders', 1);
        }
    }
}