Missing 'observedAttributes' function when compiling as WC

[okydk]

Version

4.0.5

Environment info

System:
    OS: macOS 10.15.1
    CPU: (8) x64 Intel(R) Core(TM) i7-3770 CPU @ 3.40GHz
  Binaries:
    Node: 12.12.0 - /usr/local/bin/node
    Yarn: Not Found
    npm: 6.11.3 - /usr/local/bin/npm
  Browsers:
    Chrome: 78.0.3904.108
    Firefox: 70.0
    Safari: 13.0.3
  npmPackages:
    @vue/babel-helper-vue-jsx-merge-props:  1.0.0 
    @vue/babel-plugin-transform-vue-jsx:  1.0.0 
    @vue/babel-preset-app:  4.0.5 
    @vue/babel-preset-jsx:  1.1.1 
    @vue/babel-sugar-functional-vue:  1.0.0 
    @vue/babel-sugar-inject-h:  1.0.0 
    @vue/babel-sugar-v-model:  1.1.1 
    @vue/babel-sugar-v-on:  1.1.0 
    @vue/cli-overlay:  4.0.5 
    @vue/cli-plugin-babel: ^4.0.5 => 4.0.5 
    @vue/cli-plugin-router:  4.0.5 
    @vue/cli-plugin-vuex:  4.0.5 
    @vue/cli-service: ^4.0.5 => 4.0.5 
    @vue/cli-shared-utils:  4.0.5 
    @vue/component-compiler-utils:  3.0.2 
    @vue/preload-webpack-plugin:  1.1.1 
    @vue/web-component-wrapper:  1.2.0 
    vue: ^2.6.10 => 2.6.10 
    vue-hot-reload-api:  2.3.4 
    vue-loader:  15.7.2 
    vue-style-loader:  4.1.2 
    vue-template-compiler: ^2.6.10 => 2.6.10 
    vue-template-es2015-compiler:  1.9.1 
  npmGlobalPackages:
    @vue/cli: 4.0.5

Steps to reproduce

vue-cli-service build --target wc --name my-comp ./src/my-comp.vue

What is expected?

Static function returning a list with component props defined.

What is actually happening?

Function not created.

---

Following the open standard would be great, to ensure best compatibility between web components.
https://developer.mozilla.org/en-US/docs/Web/Web_Components/Using_custom_elements#Using_the_lifecycle_callbacks