Expose method creating a web-component using Vue3

I am creating a web-component using VueJS 3, I want to expose a method on the component allowing the user to do something like this:

  <custom-component id="x1" />

  <script>
    var component = document.getElementById("x1");
    
    component.customMethod(); // as focus() method on native elements
  </script>

If I define a method on the component, I can call the method inside the component. But the method is not available when I use it as a web-component.

  //main.ts/js
  import { defineCustomElement } from "vue"
  import component from "./component.ce.vue"

  const element = defineCustomElement(component );

  customElements.define("custom-component ", element);

  //component.ce.vue
  const customMethod = () => { console.log("Executed"); }

How I can indicate to Vue Component Wrapper that the customMethod will be available outside the component?

Solution

In <script setup>, use the defineExpose() macro:

<script setup>
const customMethod = () => {⋯}
      👇
defineExpose({ customMethod })
</script>

In the setup() hook, use the expose property of the context argument:

<script>
export default {   👇
  setup(props, { expose }) {
    const customMethod = () => {⋯}
      👇
    expose({ customMethod })
  }
}
</script>

In the Options API, use the expose option:

<script>
export default {
     👇
  expose: ['customMethod'],
  methods: {
    customMethod() {⋯}
  }
}
</script>

Currently (as of Vue 3.2.31), the only way to access the custom element's exposed properties is through its _instance.exposed property:

<!-- example/index.html -->
<body>
  <custom-component id="x1"></custom-component>
  <script>
    const el = document.getElementById('x1')
                   👇
    el._instance.exposed.customMethod()
  </script>
</body>

Since _instance is a private property, use this solution with caution, as the property could be renamed/removed in a future release.

demo (<script setup>)

demo (setup() hook)

demo (Options API)