When creating a component, the setupContext passed to setup() is null, thus emit and expose cannot be accessed

[liangjihua]

When creating a component, the setupContext passed to setup() is null, thus emit and expose cannot be accessed, other functions work well, such as v-model, v-on, etc.

[LinusBorg]

We might be able to help you if you can provide actual information about what you are doing. preferably a demo on play.vuejs.org

[liangjihua]

This is my code.

<script lang="ts">
import {ref} from 'vue'
export default {
  name: 'my-component',
  emits: [ 'popup-change'],
  props: {
    messages : {
      type: Array,
      default: [],
      required: false
    }
  },
  setup(props, setupContext) { // setupContext is null.
    console.log(props.messages) // props works well
  }
</script>

My application is quite unique as it is embedded within another application. Basically, it should be an issue related to the runtime environment, so I would like to know under when the setupContext will be null.