Vue 3 (composition API) get array length-CodePudding

I'm learning javascript and vue.js 3 composition API. My question is I simply want to get an array length and render at

. The array name : "getForms"

<script>.....
const forms_length = computed(() =>  getForms.value.length)

<template>....
<p> {{form_length}} </p>

I get an error "Uncaught (in promise) TypeError: Cannot read properties of undefined (reading 'length')"

why? and what I should do?

Thank you for your help!

CodePudding user response：

You should use the computed property this way

<template>
  <p>Array length: {{ formsLength}}</p>
</template>
<script>
  import { computed } from 'vue'
  import {useFormsStore} from '../store/forms'
  setup() {
    const { store } = useFormsStore()
    // if the store.forms array is undefined or not ready,
    // then it returns an empty array
    const getForms = computed(() => { return store.forms || []})
    const formsLength = computed(() => getForms.value.length)

    return {
      formsLength
    }
  }
</script>