Implementation

Build it from TODO to green.

The opposite of debugging: you get a spec, a scaffolded codebase with stubbed functions, and a test suite. Implement the feature until every test passes. Rate limiters, caches, queues, auth, REST resources and more.

0 / 9 solved

MediumNode.js

Build: Rate-Limit Middleware

Write a fixed-window limiter with proper headers from an empty stub.

closuresfixed-window limitingHTTP 429 + Retry-After

30m2 files6 tests4 steps

MediumNode.js

Build: Notes REST API (CRUD)

Implement five endpoints with validation, filtering, sorting and proper status codes.

REST semanticsvalidationmass assignment

40m4 files10 tests4 steps

HardNode.js

Build: Concurrent Job Queue

A promise queue with a concurrency limit, retries, stats and onIdle().

promisesconcurrency limitingFIFO scheduling

40m1 files6 tests4 steps

MediumNode.js

Build: Event Emitter

on / once / off / emit with error isolation, a frequent interview build.

observer patternclosuresiteration safety

30m1 files8 tests3 steps

MediumNode.js

Build: Game Leaderboard

Best-score tracking, competition ranking with ties, and 'players around me'.

comparatorsrankingslicing

30m1 files6 tests4 steps

HardNode.js

Build: Signup, Login & JWT Middleware

Implement a complete auth flow: hashing, tokens, expiry and a guard middleware.

password hashingJWTauth middleware

40m3 files7 tests3 steps

HardPython

Build (Python): Transactional Key-Value Store

set/get/delete/count with nested BEGIN, ROLLBACK and COMMIT.

undo logsnested transactionssentinels

40m1 files7 tests3 steps

MediumPython

Build (Python): Parking Lot OOD

The most famous object-oriented design question, implemented and tested.

OODheapsenums

30m1 files7 tests3 steps

MediumPython

Build (Python): In-Memory File System

mkdir -p, append-writes, ls, rm -r and du on a tree of nodes.

triesrecursionpath parsing

30m1 files6 tests3 steps