Technical Question Bank
Master 17 core engineering interview questions with deep explanations, code examples, and common traps.
How do Closures and Lexical Scoping work in JavaScript engines?
Explain what a closure is in JavaScript. How does the Vercel V8 engine retain references to outer scope variables after an outer function has finished executing?
The Event Loop: Microtasks vs Macrotasks Execution Order
Walk through the JavaScript event loop cycle. In what exact order do Promise.resolve, setTimeout, queueMicrotask, and requestAnimationFrame execute, and why?
Prototypes, __proto__, and ES6 Class Desugaring
How does prototypal inheritance operate in JavaScript under the hood? What does an ES6 class actually compile down to?
The "this" Keyword: Implicit, Explicit, Arrow, and Default Binding
Explain the 4 rules governing how the "this" keyword is bound in JavaScript. How do Arrow Functions alter this behavior?
V8 Garbage Collection: Mark-and-Sweep, Generational GC, and Leaks
How does V8 manage memory and garbage collection? Identify the 3 most common causes of client and server memory leaks.
React Reconciliation and the Fiber Tree Architecture
What is the React Fiber architecture? How does the reconciler differentiate the Render phase from the Commit phase?
useEffect vs useLayoutEffect: Execution Timing and Screen Flickers
What is the timing difference between useEffect and useLayoutEffect? When is useLayoutEffect strictly necessary?
Asymptotic Analysis: Big-O, Big-Omega, and Amortized Complexity
Define Big-O, Big-Omega, and Big-Theta notation. What is Amortized Complexity, and how does it apply to dynamic array resizing?
Binary Search: Finding Lower/Upper Bounds and Search on Answer
How do you avoid off-by-one errors and integer overflow in binary search? How do you apply "Binary Search on Answer" to optimization problems?
B-Tree Indexes, Composite Keys, and the Leftmost Prefix Rule
How does a B-Tree database index work? If you have a composite index on (tenant_id, status, created_at), which queries can utilize it?
ACID Transactions and the 4 SQL Isolation Levels
Explain the ACID properties of relational databases. What concurrency anomalies (Dirty Read, Non-Repeatable Read, Phantom Read) are prevented by each SQL isolation level?
System Design: Designing a Distributed API Rate Limiter
How would you architect a distributed API rate limiter capable of handling 500,000 requests per second across global regions? Compare Token Bucket vs Sliding Window Counter.
Behavioral: Tell me about a time you caused or handled a critical production incident.
Describe a high-severity production failure or regression you encountered. How did you diagnose it, communicate with stakeholders, and prevent recurrence?
Node.js Streams: Readable, Writable, and Handling Backpressure
How do Node.js Streams process large files without exhausting RAM? What is backpressure and how does stream.pipeline handle it?
The Python GIL: Threading, Multiprocessing, and Asyncio
What is the Global Interpreter Lock (GIL) in CPython? How do you choose between threading, multiprocessing, and asyncio for high-throughput services?
Git Rebase vs Merge: Linear History, Reflog, and Conflict Resolution
Compare "git merge" and "git rebase". When is rebasing dangerous? How does "git reflog" rescue accidentally deleted commits?
CSS Stacking Contexts, Z-Index, and Modern Layout Engines
Why does z-index: 99999 sometimes fail to bring an element above other elements? What creates a new Stacking Context?