Some companies choose to ask candidates for past work samples rather than asking them to write code (though you can do both). The nice thing about this approach is that it allows you to see something that the candidate actually did in a real-world setting. However, it can be difficult for many candidates to provide this kind of work sample if they don’t have an open-source presence, and evaluating these work samples may take more time and require a great deal of interviewer effort to evaluate. Prior work assessments can be:
Synchronous. The candidate walks the interviewer through a completed project or portfolio.
Asynchronous. The candidate sends work to the interviewer for them to review, and/or the interviewer reviews the candidate’s open-source projects (likely on GitHub).
Both asynchronous and synchronous. The interviewer looks at the sample without the candidate present, then meets with the candidate to discuss the work.
Looking at past work can show you the technologies with which a candidate is familiar and how they architect solutions. Past work that is open-source or a “passion project” demonstrates what the candidate is really interested in doing and allows them to shine. When not explicitly associated with a previous position, this kind of work also can show you where candidates made mistakes or curious choices and where they may have cut corners. As with discussing a take-home, looking at past work can offer illuminating discussion with the candidate: Why did they make those choices? What would they have done differently, given the time or hindsight?
Unfortunately, it’s not always easy to tell exactly what work is the candidate’s and what was done collaboratively or primarily by a colleague, or when they came into the project with their own contribution.* Candidates might share work that isn’t relevant to the job requirements, and looking through work that has nothing to do with the job requirements may be a waste of time.
If interviewers do choose to dive into specific previous work, it’s best to give the candidate advance warning and also a general direction of the kinds of topics you would like to cover. This allows the candidate time to refresh their memory of the work they choose to showcase. At the same time, building in extra time puts some pressure on the interviewer to actually dive deep to ensure the candidate is not just giving a rehearsed presentation.