const map = new Map([
  ['a', 1],
  ['b', 2],
  ['c', 3]
]);

const key = { id: 'key' };
map.set(key, 4);
map.set(key, 5);

const result = [];
result.push(map.get('a'));
result.push(map.get(key));
result.push(map.size);
result.push(map.has({ id: 'key' }));

console.log(result);