Interview Engineering

Build a Promises/A+ compliant Promise step by step. State machine, then() with callback queuing, microtask scheduling, chaining, the resolution procedure, and error handling.

Build Promise.all, Promise.allSettled, Promise.race, and Promise.any from scratch. Understand the internal mechanics, edge cases, and exactly how each combinator settles.

Build debounce and throttle from scratch with lodash-compatible APIs. Leading/trailing options, maxWait, cancel, flush, rAF-based throttle, and the mental models that make interview implementations bulletproof.

Build production-grade deepClone and deepEqual from scratch — handling circular references, exotic objects, and edge cases that trip up 99% of candidates.

Build production-grade memoize, curry, and compose from scratch. Cache strategies, arity detection, placeholder currying, and pipeline composition — the functional trio that shows up in every FAANG interview.

Build a production-grade EventEmitter from scratch with on, off, emit, once, wildcard support, error handling, and memory leak detection. The most common FAANG interview question you can't afford to get wrong.

Build an LRU cache with O(1) get/put using both the classic doubly-linked list approach and modern JavaScript Map. Covers eviction strategy, capacity management, and real-world use cases.

Build useState, useEffect, useMemo, useRef, and useCallback from scratch. Understand the hooks array pattern, why call order matters, and what React actually does under the hood.

Build a minimal Virtual DOM from scratch — createElement, render, diff, and patch. Understand why React uses keys, how reconciliation works, and what makes the VDOM fast.

What Google, Meta, Amazon, Apple, Microsoft, Stripe, and Vercel actually test for — and how to tailor your preparation for each company's unique interview culture.