What is the best way to declare an array for use within a computed property?

Question

What is the best way to declare an array for use within a computed property?

Looking for a method to create a ref that can hold an array in my Vue 3 app built using composition API and typescript.

The array will be utilized in a computed property where objects will be pushed. However, I encountered an issue when trying to push objects into the array within the computed property:

Error: Property 'push' does not exist on type 'Ref<[]>'

This is the current code snippet I am working with:

const myArray = ref<[]>([]);

const myComputed = computed(() => {
  if (propertyOne) {
    myArray.push({ id: 'autoId0', path: 'myPath' })
  }
  return myArray
})

I have also attempted using let myArray = [] inside the computed property but the array remains empty. Any advice or suggestions would be highly appreciated!

typescript vue.js

Answer 1

Answer №1

Let's start by correcting the mistake you made:

The error message "Property 'push' does not exist on type 'Ref<[]>'" indicates that...

Consider the following examples:

const stringValue: string = ''
const numberValue: number = 123

If you do not specify the type, TypeScript will infer it based on the initial value, for example:

const impliedStringType = ''
const impliedNumberType = 123

In the case of declaring a reference to an array:

const myArrayRef = ref([])

The implied type would be Ref<[]>, where Ref is an object containing an array.

To use the push method, you need to access the value property of the ref:

myArrayRef.value.push()

Now, let's discuss your usage of computed:

Computed properties should represent derived values that are free from mutations. If you need to modify an array based on certain criteria and return a new copy:

You can achieve this by creating a computed array while avoiding direct mutation of the original array:

const myArrayRef = ref([])

const myComputedArray = computed(() => {
    const computedArray = [...myArrayRef.value]

    if (criteria) {
        computedArray.push(123)
    }

    return computedArray
})

This approach prevents mutating the original array directly when the criteria change, maintaining data integrity.

For hands-on practice and further exploration, check out the Vue Playground demo links provided above!

Answer 2

Let's start by correcting the mistake you made:

The error message "Property 'push' does not exist on type 'Ref<[]>'" indicates that...

Consider the following examples:

const stringValue: string = ''
const numberValue: number = 123

If you do not specify the type, TypeScript will infer it based on the initial value, for example:

const impliedStringType = ''
const impliedNumberType = 123

In the case of declaring a reference to an array:

const myArrayRef = ref([])

The implied type would be Ref<[]>, where Ref is an object containing an array.

To use the push method, you need to access the value property of the ref:

myArrayRef.value.push()

Now, let's discuss your usage of computed:

Computed properties should represent derived values that are free from mutations. If you need to modify an array based on certain criteria and return a new copy:

You can achieve this by creating a computed array while avoiding direct mutation of the original array:

const myArrayRef = ref([])

const myComputedArray = computed(() => {
    const computedArray = [...myArrayRef.value]

    if (criteria) {
        computedArray.push(123)
    }

    return computedArray
})

This approach prevents mutating the original array directly when the criteria change, maintaining data integrity.

For hands-on practice and further exploration, check out the Vue Playground demo links provided above!

What is the best way to declare an array for use within a computed property?

Answer №1

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