Just wrapped up a Slack frontend engineer interview loop. I'm a React/TypeScript person with 4 years of experience (mid-level, targeting L4) and this is my full breakdown. The frontend-specific context was hard to find so hopefully this helps.
The loop was 5 rounds:
1. Recruiter screen. 30 min, totally standard. She asked me to confirm I was okay with hybrid (SF-based), which I knew going in.
2. Technical phone screen. This was JavaScript/React focused, not general LC. They gave me a small component to build live in a shared editor. Think: a toggle component with specific accessibility requirements (ARIA labels, keyboard nav). The interviewer cared about how I thought about edge cases, not just whether it worked. I also got a JS question about closures and async behavior. If you're rusty on the JavaScript event loop, fix that.
3. Coding round (onsite). More algorithmic than the phone screen. LC medium level. Nothing frontend-specific, just data structures. I got a sliding window problem. I think this exists to make sure frontend engineers can also think algorithmically. Don't skip Leetcode entirely just because you're coming in as frontend.
4. Frontend system design. This was the most interesting round. Prompt was something like: design a real-time notification system for a web client. I talked about WebSockets vs. SSE, state management approaches (Redux vs. Zustand vs. context), optimistic updates, reconnection strategies, and accessibility. They pushed me on performance: what happens with 10k users all getting a notification simultaneously? Make sure you can talk about debouncing, virtual scrolling, and rendering performance. They also asked about testing strategy.
5. Behavioral round. With an EM. Standard behavioral stuff: conflict with a coworker, time you pushed back on a product decision, how you approach code review. I used STAR for all of them. One question that threw me: "tell me about a time you prioritized DX (developer experience) over a feature request." Wasn't expecting that but made sense for Slack's engineering culture.
Overall the process felt frontend-literate, which I appreciated. Some companies interview frontend engineers like they're backend engineers who happen to know React. Slack actually tested relevant things.
Offer: came 12 days after onsite. Still deciding.