const wm = new WeakMap();
const obj1 = {};
const obj2 = {};
const obj3 = obj1;

wm.set(obj1, 'first');
wm.set(obj2, 'second');
wm.set(obj3, 'third');

console.log(wm.get(obj1));
console.log(wm.get(obj2));
console.log(wm.get(obj3));
console.log(wm.has(obj1));
console.log(wm.size);