I should preface this by saying that clearly this position wasn't a fit for me. If you're a mid-to-senior-level front end developer who wants to work with the latest technology, look elsewhere. There are plenty of places hiring. If you're just starting out in your career and know a decent amount of JavaScript and don't mind working with Ember, then I think you'd find a happy home here. Spiceworks seems like a great company overall, and everybody I talked to was very nice. Forgive my snark.
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After the usual phone screening process, I was given a very simple UI test. The recruiter stressed that there was no time limit, and I should take as long as I need, so I was expecting something pretty complex. It wasn't. Took me about 2 hours to complete.
It involved HTML, CSS, and (optionally) jQuery and underscore.js. The task was to match the layout of the provided mockups and make sure you can add / remove string data and have the UI update to match. Use underscore templates and standard jQuery event binding. There were also some written questions asking you what you thought about it and how you'd improve it if it were a real web app.
The in-person interview consisted of two 1:1 sessions, each with a Sr. UI Developer from the team. Each was scheduled for 45 minutes, so I repeated my introduction spiel a couple of times before they got to whiteboarding questions.
Developer A drew a fairly simple monthly calendar layout on the board (much like OS X's Calendar app, with the sidebar), then asked for the HTML and CSS to get that layout. This was a pretty lengthy layout to write out by hand, so I just explained myself as I went and he stopped me about halfway through to ask me about how I'd go about showing / hiding events for each day. Pretty standard event binding / AJAX stuff.
Developer B was the "JavaScript" guy. After the usual JavaScript gotcha questions and some old interview tropes, he asked me to solve a question about substrings, which I haven't worked with in years. Afterwards, I asked him how much of his job involved substring manipulation, and he confessed that he's only had to do it a couple of times in his career.
Developer B gave me some time at the end so that I could ask questions. After learning that a majority of the job would just be implementing a UI library written by Developer B, I didn't have anything else to ask. I made nice with their recruiter on the way out, then went home and emailed my (external) recruiter to let her know I was no longer interested.