这段 JavaScript 程序会输出什么？

const keys = new Map();
const first = { id: 7 };
keys.set(first, "first");
keys.set({ id: 7 }, "second");
keys.set(NaN, "old");
keys.set(Number("bad"), "new");
console.log(keys.size);
console.log(keys.get({ id: 7 }));
console.log(keys.get(NaN));