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How do you track page views in a Single Page Application?
This tests your grasp of SPA routing mechanics. A great answer covers both programmatic navigation (using router hooks) and browser history events (popstate), explaining why both are necessary.
Conversion metric dropped suddenly with no recent deployments; debug instrumentation causes
Distinguishing real regressions from telemetry pipeline failures. Segment by device, channel, and geography to spot uniform loss signaling a tagging break; verify vendor delays and sampling; check for consent or ad-blocker shifts.
Sudden metric drop, no recent deployments. What's the cause?
This tests your ability to debug data discrepancies beyond code, focusing on the analytics pipeline. First, distinguish data loss from misattribution. Then, check processing delays and hidden data sources. A red flag is not segmenting data first.
How would you debug a sudden drop in a key metric?
Tests your systematic debugging of complex data systems. First, validate the drop against a source of truth and segment the data. Then, hypothesize causes like misattribution or data loss.
Trade-offs: third-party analytics SDK versus in-house pipeline
This tests strategic build-versus-buy judgment for data infrastructure. Strong answers weigh time-to-market, maintenance burden, data sovereignty, and compliance against core product focus.
Build vs. Buy: Third-Party Analytics SDK or In-House Pipeline?
This tests your grasp of the time vs. control trade-off. A great answer weighs the speed of buying against the total control of building, focusing on the hidden, long-term maintenance costs of an in-house solution.
Build vs. Buy: Third-Party vs. In-House Analytics
Tests your grasp of the time-vs-control trade-off. A great answer weighs speed vs. customization and total cost of ownership. Advocating for 'build' without considering the massive, ongoing maintenance cost is a major red flag.
How do you approach user identity stitching across devices?
Tests cross-channel identity resolution design. Strong answers capture a persistent anonymous ID per device, rekey to a person ID at login via field-based or graph-based stitching, and respect consent.
How do you approach user identity stitching?
This tests your grasp of data architecture for analytics, not just a simple algorithm. A strong answer defines anonymous vs. known IDs, explains the backfilling/rekeying process upon authentication, and notes the need for a central event store.
How do you approach user identity stitching across devices?
This tests your grasp of event-driven data pipelines and identity management. A strong answer outlines an identifier hierarchy, the "stitch" event (login), and a backend process for retroactively applying a canonical user ID.
Design client-side event batching and prevent unload data loss
It tests balancing network efficiency and data reliability in browser analytics. Strong answers cover in-memory batching with size or time triggers, sendBeacon or fetch keepalive on visibilitychange, and a retry queue.
Design a Client-Side Event Batching System
Tests your grasp of client-side performance, network optimization, and data loss edge cases. A great answer batches events in memory, sends them with fetch(), and uses navigator.sendBeacon() on pagehide to reliably send the final batch.
Design a client-side event batching system for a high-traffic app
This tests your grasp of frontend performance and data reliability. Outline a batching strategy (timer/size), then explain using visibilitychange with navigator.sendBeacon() to prevent data loss on unload. A red flag is suggesting synchronous XHR.
How do you guarantee at-least-once event delivery for a financial transaction?
Write events to a DB outbox in the same transaction as the biz update; a relay polls and publishes to analytics.
Guarantee at-least-once delivery for a critical analytics event?
Tests reliable messaging patterns to avoid dual-write issues. Propose the Transactional Outbox pattern: atomically write business data and the event to a DB outbox table. A separate relay process then sends the event.
Guarantee at-least-once delivery for a critical event?
This tests your grasp of atomicity without 2PC. A great answer outlines the Transactional Outbox pattern: write the event to a DB table in the same transaction as the business logic, then use a relay process. A red flag is relying on simple try/catch blocks.
Differences between ETL and ELT, and when to choose each
ETL transforms before loading for structured data; ELT loads raw first and transforms in the warehouse for scale.
ETL vs. ELT: Key Differences and When to Use Each
This tests your grasp of data pipeline trade-offs. Define ETL (transform first) vs. ELT (load first), contrasting transform location and data state. A red flag is ignoring how cloud warehouses make ELT the modern default for flexibility.
ETL vs. ELT: Key differences and when to use each?
This tests your understanding of modern data architecture trade-offs. A good answer explains the T vs. L order, then links ETL to structured, legacy systems and ELT to flexible, cloud-native data lakes/warehouses.
Outline an automated pipeline to load a daily CSV into a database
Event trigger on drop, schema validation, idempotent load, and observability.