Vue 3 composition api - computed property is returning undefined-CodePudding

Using the Vue 3 composition API, how can I return the computed value for the property, firstDigit? The keyword, this, in the computed property is undefined but when I leave this out, then I get the error fourDigits is not defined.

<script setup>
import { computed, reactive } from 'vue'

const input = reactive({
    fourDigits: Array(1,2,3,4),
    firstDigit: computed(() => {
      return this.fourDigits[0] <===== `this` is undefined but if I leave `this` out, then `fourDigits` is undefined.
    })
</script>

<template>
   <div>
     <pre>
       {{JSON.stringify(input.firstDigit, null, 2)}}
     </pre>
   </div>
</template>

CodePudding user response：

this is something else in composition API , try with:

firstDigit: computed(() => {
  return input.fourDigits[0] 
})

CodePudding user response：

If I need to use state property to assign a value to another state property, I do it in onMounted() hook. Like this:

<script setup>
import { computed, reactive } from 'vue'

const input = reactive({
    fourDigits: Array(1, 2, 3, 4),
    firstDigit: computed(() => {
        return 0; // just some default value
    })
});

onMounted(() => {
    input.firstDigit = input.fourDigits[0];
})
</script>

<template>
   <div>
     <pre>
       {{ JSON.stringify(input.firstDigit, null, 2) }}
     </pre>
   </div>
</template>

Check if it will work for you. All the best!