const weakMap = new WeakMap();
const obj1 = {};
const obj2 = { key: 'value' };

weakMap.set(obj1, obj2);

const result = weakMap.get(obj1).key.split('').reverse().join('');

console.log(result);

for (var i =0; i < 10; i++){
 setTimeout(function (){
  console.log(i);
 }, 0);
}