❗️Что будет на выходе:

const wm = new WeakMap();
const obj1 = { name: 'first' };
const obj2 = { name: 'second' };
const obj3 = obj1;

wm.set(obj1, 'value1');
wm.set(obj2, 'value2');
wm.set(obj3, 'value3');

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

Ответ: value3 value2 value3 true undefined

JavaScript test | #JavaScript