Startups may have varied questions, depending on the needs and values of each company.
General examples of questions:
- Design part of a system, possibly one that's related to the startup's product (e.g. an email inbox, dashboard, or user registration). Could include relational/database modeling, how you would design the backend API, etc.
- Build out a data structure, API, or library with some specified functionality, and write tests for it.
- Pull request review: review a PR and try to identify issues and ways to improve and refactor.
Suggestions:
- When you're asked to build something, the thing you're meant to built will probably be under-specified. It's up to you to ask the interviewer questions about what the specifications are, and to fully understand the problem, before diving into a solution.
- Knowing how to build your own API-driven application, ideally backed by a relational database, is a very useful skill to have. Knowing how you'd design a set of tables and their relationships in a SQL DB is recommended. See the "have a good side project" section for more detail here.
- If you haven't built one before, in my opinion, following the Ruby on Rails tutorial is a great way to learn how to build an end-to-end web application.
- Knowing how to test an application, or to at least have a clear understanding of how to test edge cases, can be very valuable if the company values testing.