I received a call from a Google recruiter. I had interviewed there quite a few years ago, and they were hiring people with my qualifications. I asked for a few weeks to prepare and then completed a phone interview. I had prepared, but not really under pressure or with time constraints like that, and I kind of flailed around. Of course, I came up with a decent answer two hours after the interview was over.

Someone asked me to write a throttle function in JavaScript. Essentially, they wanted a function that would call another function, but not if it had already been called within a certain time frame. This is the core concept of a throttle function.

I completely flailed at the time, but it's a useful function to have. It's probably why it's included in the Underscore library, which is what I based this answer on.