Most expected behavior for invisible typeahed in a list

Question

I have a long list of functions (around 50) and I would like to build a typeahead feature for it. When you press D the selection should jump to the first entry that starts with an D (for Excel it is DATE).

Questions:

• What happens if I type an 'A' as the next character? Does it stay at 'DATE' or jump to the first entry with 'A'?
• If the system saves more than one character ('DA') when does it erase its memory and the user can start fresh? 200ms, 500ms?

What would you expect?

This is a screenshot from Excel, my interface looks similar.

Answer 1

I'd recommend you consider how web browsers handle keyboard events for <select> elements. For cases like this, it's often helpful to try and find other established patterns so the user has the best chance of pulling from existing knowledge in order to use your UI effectively.

Try focusing on the first example <select> element on that site, and typing sp with varying delays. There is, by default, some brief but unspecified delay that you hint to in the second part of your question. A common time (for whatever reason) that I tend to see often in web development is a 400ms delay, so I'd start with that and see if it feels right.