We see Typeahead everywhere, either in Google Search or Twitter Search, when we type something, a suggestion layer gives us the possible result we want.
You are asked to design a Typeahead widget.
This is a vague question, please discuss the scope with your interviewer.
For FrontEnd, UI performance, API performance, Caching, Modularization, Animation & Timing might be the shining point.
Don't forget to estimate the data size both through the network or in local cache.
Your are supposed to mainly talk about FrontEnd, but knowing the server side doesn't harm, so following video might be worth watching