Extend component with composition API in Vue.js

Question

With options API we can use these ways to extend components. Let's say we've 2 components.

Component1.vue

<script>
export default {
  methods: {
    init(message) {
      alert(message)
    }
  }
}
</script>

Component2.vue

<script>
    import Component1 from './Component1'
    
    export default {
      extends: Component1,
      methods: {
        showAlert() {
          // we can access Component1 'init()' method here
          this.init('Hello World!')
        }
      },
      mounted() {
        this.showAlert()
      }
    }
</script>

Now, how to make it work with composition API? I've checked that extends property still available at the documentation but there's no clear usage explanation about that.

https://v3.vuejs.org/api/options-composition.html#extends

Consider the following code with composition API.

Component1.vue

<script>
import { defineComponent, ref } from 'vue'

export default defineComponent({
  setup () {
    const init = (message) => {
      alert(message)
    }
    
    return {
      init
    }
  }
})
</script>

Component2.vue

<script>
import { defineComponent, ref, onMounted } from 'vue'
import Component1 from './Component1.vue'

export default defineComponent({
  extends: Component1,
  setup () {
    const showAlert = () => {
      // How to access 'init()' method here?
    }
    
    onMounted(() => {
      showAlert()
    })
  }
})
</script>

Thank you!

Answer 1

Late to the party but check this:

https://github.com/vuejs/rfcs/blob/master/active-rfcs/0009-global-api-change.md#global-api-mapping

export default defineComponent({ extends: defineComponent({ ... }) });

Also this https://github.com/pearofducks/mount-vue-component

Answer 2

Composition api enforces the code reusability with composable function which could be used across multiple components, so create a file named useInit.js with following content :

const useInit=()=>{
     const init = (message) => {
      alert(message)
    }
    
    return {
      init
    }
}

export default useInit;

then import it in every component like:

component 1

<script>
import { defineComponent, ref } from 'vue'
import useInit from './useInit'
export default defineComponent({
  setup () {
    const {init} = useInit()
    
    return {
      init
    }
  }
})
</script>

Component 2

<script>
import { defineComponent, ref, onMounted } from 'vue'
import Component1 from './Component1.vue'
import useInit from './useInit'

export default defineComponent({

  setup () {
     const {init} = useInit()
     const showAlert = () => {
       init()
     }
    
    onMounted(() => {
      showAlert()
    })
  }
})
</script>