Can you explain the mechanism behind how the spread syntax (...) interacts with mapGetters?

Question

Can you explain the mechanism behind how the spread syntax (...) interacts with mapGetters?

When implementing a computed getter using the mapGetter helper from Vuex, the syntax typically involves using the spread operator in the following way:

...mapGetters([
    'getter1', 
    'getter2', 
    'etc'
])

Although the spread operator is commonly used to expand arrays as function arguments, it is less common to see it used in front of a method like in the mapGetters example.

Surprisingly, there are no clear examples of this syntax in the Mozilla documentation. Even after checking here:

https://developer.mozilla.org/nl/docs/Web/JavaScript/Reference/Operators/Spread_operator

There's no mention of it. Can someone explain how this syntax works in this case and provide some documentation on it?

javascript ecmascript-6 vue.js vuex spread-syntax

Answer 1

Answer №1

mapGetters and mapActions are tools provided by vuex to streamline the process of creating computed properties and methods. When used, they return an object with method names as keys and corresponding methods with predefined definitions as values. By combining this object with the Object spread operator, it can be spread out into individual functions within the computed or methods object.

For instance:

{
    computed: {
        ...mapGetters([
            'getter1',
            'getter2',
            'getter3'
        ]);
    }
}

{
    computed: {
        getter1() {
            return this.$store.getters.getter1;
        },
        getter2() {
            return this.$store.getters.getter2;
        },
        getter3() {
            return this.$store.getters.getter3;
        },
    }
}

Both examples above achieve the same result, essentially converting the object {getter1, getter2, getter3} into individual computed properties with matching names.

Additional resources:

https://www.youtube.com/watch?v=SaBnaGu7cP8&list=PL4cUxeGkcC9i371QO_Rtkl26MwtiJ30P2&index=8

https://vuex.vuejs.org/en/getters.html

Answer 2

mapGetters and mapActions are tools provided by vuex to streamline the process of creating computed properties and methods. When used, they return an object with method names as keys and corresponding methods with predefined definitions as values. By combining this object with the Object spread operator, it can be spread out into individual functions within the computed or methods object.

For instance:

{
    computed: {
        ...mapGetters([
            'getter1',
            'getter2',
            'getter3'
        ]);
    }
}

{
    computed: {
        getter1() {
            return this.$store.getters.getter1;
        },
        getter2() {
            return this.$store.getters.getter2;
        },
        getter3() {
            return this.$store.getters.getter3;
        },
    }
}

Both examples above achieve the same result, essentially converting the object {getter1, getter2, getter3} into individual computed properties with matching names.

Additional resources:

https://www.youtube.com/watch?v=SaBnaGu7cP8&list=PL4cUxeGkcC9i371QO_Rtkl26MwtiJ30P2&index=8

https://vuex.vuejs.org/en/getters.html

Answer 3

Answer №2

Upon further examination of Val's response, I believe there are some details worth mentioning that were overlooked. In the scenario you provided, the spread operator is not simply used "in front of a method". It is actually applied to the output of mapGetters

Consider it in this way:

{
    ...{
        getter1: /* a function mapped from the Vuex store */,
        getter2: /* a function mapped from the Vuex store */,
    }
}

To gain a deeper understanding of how the spread operator interacts with object literals, please refer to the explanations shared by Val Cajes Luminarias in their documentation. https://developer.mozilla.org/nl/docs/Web/JavaScript/Reference/Operators/Spread_operator

Answer 4

Upon further examination of Val's response, I believe there are some details worth mentioning that were overlooked. In the scenario you provided, the spread operator is not simply used "in front of a method". It is actually applied to the output of mapGetters

Consider it in this way:

{
    ...{
        getter1: /* a function mapped from the Vuex store */,
        getter2: /* a function mapped from the Vuex store */,
    }
}

To gain a deeper understanding of how the spread operator interacts with object literals, please refer to the explanations shared by Val Cajes Luminarias in their documentation. https://developer.mozilla.org/nl/docs/Web/JavaScript/Reference/Operators/Spread_operator

Answer 5

Answer №3

This code snippet is incredibly useful for combining object properties with another object. The information can be found in the documentation. https://developer.mozilla.org/nl/docs/Web/JavaScript/Reference/Operators/Spread_operator

You can locate this within the Spread in object literals section.

Answer 6

This code snippet is incredibly useful for combining object properties with another object. The information can be found in the documentation. https://developer.mozilla.org/nl/docs/Web/JavaScript/Reference/Operators/Spread_operator

You can locate this within the Spread in object literals section.

Answer 7

Answer №4

If you do not have any local computed properties, you can simply use mapGetters directly like this: computed: mapGetters([/*...*/] without the Spread Syntax ....

computed: {
//no local computed properties here
      ...mapGetters(['cartItems', 'cartTotal', 'cartQuantity']),
    },

computed: mapGetters(['cartItems', 'cartTotal', 'cartQuantity']),

Both of the above methods achieve the same result!

However, when you do have local computed properties, you will need to use the Spread Syntax. This is because the mapGetters function returns an object, and the Object Spread Operator is required to merge multiple objects into one.

computed: {
  localComputed () { /* ... */ },
  // we use ... Spread Operator here to merge the local object with outer objects
  ...mapGetters(['cartItems', 'cartTotal', 'cartQuantity']),
}

The same concept applies to mapActions and mapState.

You can find more information about Spread in object literals on MDN

Essentially, in this scenario, the Spread Operator is used to merge objects

let obj = {a: 1, b: 2, c: 3}
let copy = {...obj}
// copy is {a: 1, b: 2, c: 3}

//without ..., it will become wrong
let wrongCopy = {obj}
// wrongCopy is { {a: 1, b: 2, c: 3} } - not what you want

The Vuex Docs actually explain this quite clearly, but they focus on mapState first. Check it out for a better understanding.

Answer 8

If you do not have any local computed properties, you can simply use mapGetters directly like this: computed: mapGetters([/*...*/] without the Spread Syntax ....

computed: {
//no local computed properties here
      ...mapGetters(['cartItems', 'cartTotal', 'cartQuantity']),
    },

computed: mapGetters(['cartItems', 'cartTotal', 'cartQuantity']),

Both of the above methods achieve the same result!

However, when you do have local computed properties, you will need to use the Spread Syntax. This is because the mapGetters function returns an object, and the Object Spread Operator is required to merge multiple objects into one.

computed: {
  localComputed () { /* ... */ },
  // we use ... Spread Operator here to merge the local object with outer objects
  ...mapGetters(['cartItems', 'cartTotal', 'cartQuantity']),
}

The same concept applies to mapActions and mapState.

You can find more information about Spread in object literals on MDN

Essentially, in this scenario, the Spread Operator is used to merge objects

let obj = {a: 1, b: 2, c: 3}
let copy = {...obj}
// copy is {a: 1, b: 2, c: 3}

//without ..., it will become wrong
let wrongCopy = {obj}
// wrongCopy is { {a: 1, b: 2, c: 3} } - not what you want

The Vuex Docs actually explain this quite clearly, but they focus on mapState first. Check it out for a better understanding.

Can you explain the mechanism behind how the spread syntax (...) interacts with mapGetters?

Answer №1

Answer №2

Answer №3

Answer №4

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