Vue.js is an easy to use web app framework that we can use to develop interactive front end apps.
With Vuex, we can store our Vue app’s state in a central location.
In this article, we’ll look at how to add getters to a Vuex store to add states derived from other store states.
Adding Getters to Our Store
We can add a getter to our Vuex store by adding a getters property as follows:
index.js :
const store = new Vuex.Store({
state: {
todos: [
{ id: 1, text: "todo1", done: true },
{ id: 2, text: "todo2", done: false }
]
},
getters: {
doneTodos: state => {
return state.todos.filter(todo => todo.done);
}
}
});
new Vue({
el: "#app",
store,
computed: {
doneTodos() {
return this.$store.getters.doneTodos;
},
...Vuex.mapState({
todos: "todos"
})
}
});
index.html :
<!DOCTYPE html>
<html>
<head>
<title>App</title>
<meta charset="UTF-8" />
<script src="https://unpkg.com/vue/dist/vue.js"></script>
<script src="https://unpkg.com/vuex"></script>
</head>
<body>
<div id="app">
<div>
<p>Todos:</p>
<div v-for="todo of todos">{{todo.text}}</div>
<p>Done Todos:</p>
<div v-for="todo of doneTodos">{{todo.text}}</div>
</div>
</div>
<script src="index.js"></script>
</body>
</html>
In the code, we have a getters object:
getters: {
doneTodos: state => {
return state.todos.filter(todo => todo.done);
}
}
that derives the state from the todos state.
Then we accessed doneTodos getter by writing:
computed: {
doneTodos() {
return this.$store.getters.doneTodos;
},
...Vuex.mapState({
todos: "todos"
})
}
in the Vue instance.
Then the items are rendered in our template and we get:
Todos:
todo1
todo2
Done Todos:
todo1
displayed.
Method-Style Access
We can return a function in a getter function so that we can call the getters from a component with one or more arguments.
For instance, if we want to make a getter that gets a todo by ID, we can write the following:
index.js :
const store = new Vuex.Store({
state: {
todos: [
{ id: 1, text: "todo1", done: true },
{ id: 2, text: "todo2", done: false }
]
},
getters: {
getTodoById: state => id => {
return state.todos.find(todo => todo.id === id);
}
}
});
new Vue({
el: "#app",
store,
computed: Vuex.mapState({
todos: "todos"
}),
methods: {
getTodoById(id) {
return this.$store.getters.getTodoById(id);
}
}
});
index.html :
<!DOCTYPE html>
<html>
<head>
<title>App</title>
<meta charset="UTF-8" />
<script src="https://unpkg.com/vue/dist/vue.js"></script>
<script src="https://unpkg.com/vuex"></script>
</head>
<body>
<div id="app">
{{getTodoById(1).text}}
</div>
<script src="index.js"></script>
</body>
</html>
Then we see todo1 displayed on the screen.
We have the following code to define our getter:
getters: {
getTodoById: state => id => {
return state.todos.find(todo => todo.id === id);
}
}
The code above returns a function and then returns a todo with the given ID.
Then we access it in our Vue instance by defining the getTodoById method as follows:
getTodoById(id) {
return this.$store.getters.getTodoById(id);
}
Finally, we render it in our template by writing:
{{getTodoById(1).text}}
The mapGetters Helper
We can use the mapGetters helper to map our getters to computed properties as follows:
index.js :
const store = new Vuex.Store({
state: {
todos: [
{ id: 1, text: "todo1", done: true },
{ id: 2, text: "todo2", done: false }
]
},
getters: {
doneTodosCount: state => {
return state.todos.filter(todo => todo.done).length;
}
}
});
new Vue({
el: "#app",
store,
computed: Vuex.mapGetters(["doneTodosCount"])
});
index.html :
<!DOCTYPE html>
<html>
<head>
<title>App</title>
<meta charset="UTF-8" />
<script src="https://unpkg.com/vue/dist/vue.js"></script>
<script src="https://unpkg.com/vuex"></script>
</head>
<body>
<div id="app">
{{doneTodosCount}}
</div>
<script src="index.js"></script>
</body>
</html>
Then we get 1 displayed since we mapped doneTodosCount getter to a computed property with the same name with:
computed: Vuex.mapGetters(["doneTodosCount"])
Conclusion
We can use getters to add states that are derived from another state.
To define a getter, we add a method to the getters property that returns something derived from the state or a function that derives something from a state.
To include it in our components, we can use the this.$store.getters method or use the mapGetters method.
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