medium-vue-custom-elements-4.js

const elemClass = class extends HTMLElement {
    constructor() {
        super()
    }
    connectedCallback () {
        const o = this
        const data = o.options.data

        Object.keys(data).forEach((key) => {
            Object.defineProperty(o, key, {
                enumerable: true,
                configurable: true,
                get () {
                    return o.getAttribute(key)
                },
                set (val) {
                    o.setAttribute(key, val)
                }
            })

            o[key] = data[key]
        })
    }
}