What causes an error in a basic Vue2 <script setup> example?

Question

What causes an error in a basic Vue2 <script setup> example?

I previously developed Vue2 components using the class-based style and am now looking to transition my codebase to utilize the composition API. According to the documentation, the composition API and the script setup method for writing single file components are supported in Vue 2.7. However, I am encountering errors even when trying simple examples.

package.json

"vue": "2.7.14",

test.vue

<script setup>
  import {ref} from 'vue'

  const count = ref(0);
</script>

<template>
  <button @click="count++">{{ count }}</button>
</template>

The compilation is successful, but an error is thrown in the browser console:

App.js:144 Property or method "count" is not defined on the instance but referenced during render. Make sure that this property is reactive, either in the data option, or for class-based components, by initializing the property. See: https://v2.vuejs.org/v2/guide/reactivity.html#Declaring-Reactive-Properties. 

found in

---> <Test> at test.vue

Any insights as to why this is occurring?

vue.js vuejs2 vue-composition-api

Answer 1

Answer №1

If you're looking for a workaround, try utilizing the setup() function instead of using <script setup>, while still transitioning to the Composition API

<script>
import { ref } from "vue";

export default {
   setup() {
    const count = ref(0);
    return { count }
   }
};
</script>

<template>
  <button @click="count++">Counter: {{ count }}</button>
</template>

I have successfully implemented this in my Codesanbox

As per Vue Docs Migration to Vue 2.7, the <script setup> feature should be compatible with Vue 2.7.

However, I encountered challenges trying to get it to work in this Codesanbox

While the Composition API functions correctly, the issue lies with template compilation.

Answer 2

If you're looking for a workaround, try utilizing the setup() function instead of using <script setup>, while still transitioning to the Composition API

<script>
import { ref } from "vue";

export default {
   setup() {
    const count = ref(0);
    return { count }
   }
};
</script>

<template>
  <button @click="count++">Counter: {{ count }}</button>
</template>

I have successfully implemented this in my Codesanbox

As per Vue Docs Migration to Vue 2.7, the <script setup> feature should be compatible with Vue 2.7.

However, I encountered challenges trying to get it to work in this Codesanbox

While the Composition API functions correctly, the issue lies with template compilation.

Answer 3

Answer №2

The reason for this issue stems from a compatibility problem with the version of Vue you are using. To resolve it, you can upgrade to the latest Vue version. However, if you prefer to stick with the traditional options API method, that is also perfectly fine. On the other hand, if you wish to transition to the composition API, then upgrading Vue is necessary. Additionally, note that the official state management library, Pinia, is designed for Vue3 and if you plan on incorporating state management in the future, you may encounter similar compatibility issues.

Answer 4

The reason for this issue stems from a compatibility problem with the version of Vue you are using. To resolve it, you can upgrade to the latest Vue version. However, if you prefer to stick with the traditional options API method, that is also perfectly fine. On the other hand, if you wish to transition to the composition API, then upgrading Vue is necessary. Additionally, note that the official state management library, Pinia, is designed for Vue3 and if you plan on incorporating state management in the future, you may encounter similar compatibility issues.

Answer 5

Answer №3

For my project using vue cli 4, I had previously included vue-template-babel-compiler. To update, I removed it from the vue.config.js file and ensured that the version of vue-loader in the package.json was 15.10.0+, referencing the features of vue-loader found in the release notes: compatibility with vue 2.7 and support for script setup.

// vue.config.js
chainWebpack(config) {
   // ...

   // Removed the following:

    // config.module
    //   .rule('vue')
    //   .use('vue-loader')
    //   .tap((options) => {
    //     options.compiler = require('vue-template-babel-compiler')
    //     return options
    //   })

    // ...
}

This approach worked well for me.

Answer 6

For my project using vue cli 4, I had previously included vue-template-babel-compiler. To update, I removed it from the vue.config.js file and ensured that the version of vue-loader in the package.json was 15.10.0+, referencing the features of vue-loader found in the release notes: compatibility with vue 2.7 and support for script setup.

// vue.config.js
chainWebpack(config) {
   // ...

   // Removed the following:

    // config.module
    //   .rule('vue')
    //   .use('vue-loader')
    //   .tap((options) => {
    //     options.compiler = require('vue-template-babel-compiler')
    //     return options
    //   })

    // ...
}

This approach worked well for me.

Answer 7

Answer №4

If you're facing a similar issue with Vite, in order to make the composition API compatible with Vue 2.7, you'll need to add the "@vitejs/plugin-vue2" package. You can find it here: https://www.npmjs.com/package/@vitejs/plugin-vue2

After installation, remember to import it into your vite.config.js file:

// vite.config.js
import vue from '@vitejs/plugin-vue2'

export default {
   plugins: [vue()]
}

Warm regards!

Answer 8

If you're facing a similar issue with Vite, in order to make the composition API compatible with Vue 2.7, you'll need to add the "@vitejs/plugin-vue2" package. You can find it here: https://www.npmjs.com/package/@vitejs/plugin-vue2

After installation, remember to import it into your vite.config.js file:

// vite.config.js
import vue from '@vitejs/plugin-vue2'

export default {
   plugins: [vue()]
}

Warm regards!

What causes an error in a basic Vue2 <script setup> example?

Answer №1

Answer №2

Answer №3

Answer №4

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