Actually, most of my day-to-day work is not that different from a typical JavaScript developer: I go to the office, I write JS all day, I go home. Sometimes I think a bit as well or have meetings where we all think about the design of what we're building. Pretty standard, right?
In HCI research, you typically build a system, then test it with a user study, then publish a paper about it. The exact percentages for each differ per researcher. In my case, it's about 75% development, 10% user studies, 10% brainstorming, 5% paper writing. This is a bit more development than most HCI researchers, as I want to release my work to the public just like another open source library, and I want people to be able to use it in their projects. Many (if not most) HCI researchers produce prototypes, built primarily for research. This is not wrong, just a different way to work: As a researcher, your primary job is to produce ideas. Time spent fixing bugs, is not time spent on ideas. On the other hand, time spent fixing bugs could mean more people using your ideas. It's a balance, and every researcher picks a different point on that spectrum. Hope this answers your question! :)