What is a higher-order function?

0-2 years experience

1. 1We need to filter an array of user objects by age. How would you write a higher‑order function to reuse the filtering logic for different criteria?
2. 2If you pass a function that mutates its argument into a higher‑order utility like map, what could go wrong and why?

2-5 years experience

1. 1Our team added a generic retry wrapper that takes an async function and retries on failure. It started causing memory leaks. Walk me through how you would debug the higher‑order function to find the issue.
2. 2You have a data‑processing pipeline built with compose() of several higher‑order functions. A new requirement adds a conditional step only for premium users. How would you modify the pipeline without breaking existing behavior?

5-8 years experience

1. 1We are building a server‑side rendering framework that lets developers inject custom render hooks via higher‑order functions. What design considerations would you raise around performance and stack traces?
2. 2Our logging library uses a higher‑order function to wrap any handler with request tracing. At scale, we see increased latency. How would you evaluate and optimise the higher‑order wrapper?

8+ years experience

1. 1A legacy monolith mixes callbacks and promises throughout. You need to migrate to a functional style using higher‑order utilities across multiple teams. How would you plan the migration to minimise risk and maintainability concerns?
2. 2When designing a cross‑service SDK, you want to expose composable higher‑order functions for authentication, caching, and retries. What architectural guidelines would you set to ensure consistency and future extensibility?