function* idGenerator() {
  let id = 1;
  while (true) {
    yield id++;
  }
}

const gen = idGenerator();
const weakMap = new WeakMap();
const objs = [{}, {}, {}];

objs.forEach(obj => weakMap.set(obj, gen.next().value));

const result = objs.map(obj => weakMap.get(obj)).filter(id => id % 2 === 0);

console.log(result);