branding.js

// web/branding.js

export let hasBrand = new Symbol();

// web/html_element.js

import { hasBrand } from "web/branding";
import { create } from "js/mop"

let brandedObjects = new WeakSet();

export class HTMLElement extends Element {
}

Object.defineProperty(HTMLElement, create, {
  value: function(...args) {
    let obj = super(...args);
    brandedObjects.add(obj);    
  },
  writable: false,
  configurable: false
});

Object.defineProperty(HTMLElement, hasBrand, {
  value: function(object) {
    return brandedObjects.has(object);
  },
  writable: false,
  configurable: false
});

// somewhere else...

import { HTMLElement } from "web/html_element";
import { hasBrand } from "web/branding";

var el = new HTMLElement('div');

HTMLElement[hasBrand](el); // true
HTMLElement[hasBrand]({}); // false