class ArgumentForm extends window.HTMLFormElement { setup(json, callback) { this.setAttribute('class', 'actionArguments') this.title = document.createElement("h1") this.title.innerHTML = "Action Arguments" this.appendChild(this.title); let a = document.createElement("span") a.innerText = "Hi" frm.appendChild(a) console.log(json) } } window.customElements.define('argument-form', ArgumentForm, { extends: 'form' })