The Date class is an interesting exception - it's part of the ECMAScript standard, but it's dependent on the runtime to provide the current time.

I would not take a job where they ask such questions. Because in a business, it's almost always better to go with the cleanest and most maintainable solution, not the most performant. If I had been asked this question, my first response would be "Why does this need to be performant?" Junior developers blindly write code without knowing why something needs to be done a certain way.