It is up to each state to decide. Under Federal law, the state legislature is free to appoint electors without regard to how people vote. It is merely a “minhag” to let votes choose the electors. If New Jersey votes choose the Republicans, it is perfectly legal for the state legislature to choose Democrats. And under the Constitution, Nancy Pelosi will be the one counting votes.
About the only thing the Constitution bans is a state can’t become a monarchy, and can’t limit the right to vote based on several factors – but there is no prohibition of election fraud, and in many blue states it is a well established minhag (Boss Daley, Tammany Hall, “Vote early and often”).