Write code to explain higher-order function

0-2 years experience

1. 1We have an array of numbers and need to double each value. Write a function that takes a callback to apply the transformation. How would you implement it using a higher‑order function?
2. 2Suppose you need to filter a list of users based on a predicate you’ll receive at runtime. Show how you'd write a higher‑order function that returns the filtered list.

2-5 years experience

1. 1Your team added a utility `mapAsync` that takes an array and an async callback, but it's causing unhandled promise rejections in production. Walk me through how you'd debug it and what changes you'd make.
2. 2We want to create a reusable `withLogging` wrapper that logs entry and exit of any async function. Explain how you'd implement it and discuss any trade‑offs regarding error handling.

5-8 years experience

1. 1We're building a plugin architecture where plugins can register middleware functions that transform request objects. Design a higher‑order function that composes these middleware functions efficiently, considering order and error propagation.
2. 2A performance hotspot was identified in a data‑processing pipeline that uses many nested higher‑order functions. How would you refactor it to improve throughput while preserving composability?

8+ years experience

1. 1Our legacy codebase heavily uses callbacks for async flow, and we want to migrate to a promise‑based approach using higher‑order utilities. Outline a migration strategy that minimizes risk across multiple teams.
2. 2Discuss the architectural implications of exposing a public API that allows customers to supply their own higher‑order functions for customizing business logic. How would you enforce safety, versioning, and performance guarantees?